I thought it would be helpful to consolidate a list of the primary benefits of web sites/services being transparent online. If there are any I missed, please leave a comment and I'll update the list:
Benefits of Transparency (for online websites and services)
1. Build trust with your users
2. Increase loyalty, reduce churn
3. Improve perception of your reliability
4. Reduce support costs
5. Control the message
6. Gain a competitive advantage
7. More time to focus on the actual problem
8. Reduce stress
9. Learn
See below for more detail...
1. Build trust with your users
Your users have a pretty low bar for how they expect to be treated. They basically expect you to screw them, hide information from them, and do the bare minimum to take their money. If you do something good for them, something unexpected like admit that you have problems proactively, and show your humanity, your users will develop a sense of trust for your service and your company. I believe that trust may be the most important asset you can earn on the web, especially if you deal things that are really important to your customers (e.g. money, email, photos, etc.).
Example: If the car company does a recall as soon as there is a hint of a problem, you trust them a lot more then if they are forced to do a recall after a number of deaths.
The more times you are proactive and admit to problems before you are caught, the stronger the sense of trust gets. If you are instead forced to admit your problems, or your customers complain before you tell them that you are aware of the problem, the harder it gets to convince them that you know what you are doing and that you care about the quality of the service.
2. Increase loyalty, reduce churn
Your users don't expect you to be perfect. They will forgive you when you have a problem. But only if they feel that they can trust you, that you know what you are doing, and that things are improving. Your users will stick with you if they feel like you know what you are doing, that you feel their pain, that you are taking these issues seriously. Apologizing and explaining after the fact is much more difficult. It is hard to convince your customers that you know what you are doing and that you care about their issues if you avoid the problem, or worse pretend that it doesn't exist.
Example: Atlassian's security breach a few months ago...they could have lost a lot of concerned customers questioning their is trustworthy. Instead they increased loyalty and trust by being up front about the situation, explaining what they are doing about it, and improving for the future. If instead the issue was exposed independently, they would have seen a mass exodus.
A major downtime event is innately going to lead to unhappy customers. You may as well try to turn it around into something worthwhile, and try to keep as many customers as you can. A nice side benefit is that the more your users learn to trust you, the more loyal and forgiving they become. It's a powerful loop that you want to get on the right side of.
3. Improve perception of your reliability
When users run into a problem with your service, whether it's their fault or yours, they'll often assume the wrong is on your end. If you instead show them exactly when you are actually having problems, and if you do this reliably and consistently, they'll know when you really have problems, and end up seeing that you aren't down as often as they thought. It's ironic that the more open you are about how often you have a problem, the less often your users will think you really are down.
Example: A complex web applications made up of many components, say using Google App Engine, the Foursquare API, and Google ads. You get alerted about a timeout issue...will you assume that Google is at fault or one of the other components. A quick visit to Google's public dashboard would show you that they are perfectly fine, and that the problem lies with one of the other services (which need their own public dashboards).
4. Reduce support costs
During a downtime incident your support department gets flooded with the same type of question..."I'm seeing a problem, what's going on?" and "Is the site down or is it just me?". If you can allow your customers to serve themselves, or make it easy for your support department to point complaints to a single succinct explanation, they can operate much more efficiently, and focus on higher level issues.
Also, a lot of times support doesn't even know what's going on during a downtime event, and having something to check themselves gives them more insight into the health of the system
Example: Amazon Web Services barely has support. They have a paid support service, and their forums, but otherwise there is very little real-time support. They can do this because they have a real-time public health dashboard that addresses 90% of the questions users are going to have in their day-to-day use of the service.
5. Control the message
If you don't tell your users what's going on during an event, they are going to speculate and assume the worst. They'll assume you aren't aware of the problem, that it'll last a long time, and that you're not taking it seriously. Even a simple update telling users that you are aware of the problem and are working on it gives them confidence that this isn't going to be the end of the company, and that you feel their pain.
Example: Users of Twitter experience on-and-off issues, but they can always tell how healthy the service is as a whole by visiting their public dashboard and status blog. They don't have to wonder how far-reaching the downtime is, or how long it'll last.
6. Gain a competitive advantage
All else being equal, when prospects are comparing your service to a competitor, especially when your service is critical to their own life/business, being able to tell a story about being transparent and open is a powerful differentiator. It gives your prospect a feeling of control, that they won't be left in the dark when the sh** hits the fan and their boss is breathing down their neck.
7. More time to focus on the actual problem
Especially for a small company, you can spend more time dealing with resolving the issue and less time fielding calls/emails. The better your process, the less you have to worry about beyond fixing the actual problem.
8. Reduce stress
With a defined process, ideally one that is procedural, you keeps people from freaking out and having to scramble at the worst possible time. The last thing you want to be doing during a downtime event is figuring out who can say what, and how to actually contact your entire customer base about a potential problem.
9. Learn
As noted by a comment by Heather Leson in the original post, disasters are an opportunity to help both customers and company staff share in the learning process. The more open you are about your issues, the more opportunity you'll have in both learning from your customers that may have had similar experiences, and the more your customers will learn from your experience. You aren't alone. Your customers have a vested interest in helping you succeed. You may be surprised by how forthcoming they are with advice and recommendations for your situation. Google App Engine ended up adding new features after a major downtime event, no doubt based on customer feedback. Amazon added their public health dashboard after one too many outages. As Heather put it, "Mutual success is one of the cornerstones of open source/open web organizations."