Go ahead and dismiss this, but I found it valuable. It's not often that a high-profile company publishes their own uptime data, and it has a clear and useful purpose to me. When I'm planning for uptime and making agreements with our customers, it's nice to have a point of reference. In other words, if 37Signals has a hard time getting to four-nines, I would anticipate similar struggles. I may write a four-nines (or five-nines) SLA, but I'll write the penalties in a way that doesn't shoot a hole in my boat.

Yes, we have our own uptime data, but we're a young company, and we're still scaling. Coincidentally, on a similar stack to 37Signals. More data is better.