The down voting on my previous reply is sad but I probably shouldn't be too surprised. The problem of being way too technical for a mainstream audience is a problem many people on Hacker News seem to have, and so no wonder many would disagree with me.

It's silly for someone on Hacker News to say "well I thought the level of detail was fine" - of course you would, like the rest of us you're a technical geek. The point that seems to be lost is 95% of FourSquare's userbase ISN'T!

Also FourSquare is one of those startups that, in addition to the YC startups (for obvious reasons I guess), people give a little more favoritism to then perhaps other startups of equal quality/interestingness.

How do you think it could have been better? We struggled a lot trying to decide how much technical detail to include. We decided that including more information (even if a lot of our users didn't understand it) was better than "something broke, it took a long time to fix."
Would love to hear suggestions on this topic.

Well, I'm not suggesting you wrote "something broke, it took a long time to fix" - I'm all for transparency. But if you are going to be transparent you need to communicate at a level at which that transparency can be understood by all of your readers. I'm sorry if some people on Hacker News don't get that.

So ok, here's how I would have written your post (for time sake I just did the intro - I'd have repeated the technical description after this block of copy):

Yesterday, we experienced a very long downtime. All told, we were down for about 11 hours, which is unacceptably long. It sucked for everyone (including our team – we all check in everyday, too). We know how frustrating this was for all of you because many of you told us how much you’ve come to rely on foursquare when you’re out and about. For the 32 of us working here, that’s quite humbling. We’re really sorry.

Below is an explanation of what happened and what we’re doing to make sure it doesn’t happen again in the future (a more technical explanation for those inclined appears further below)

What happened
As you can imagine we store a huge amount of data from all of your user check-ins. We split that data across many servers as it's obviously far to big to fit onto just one. Starting around 11:00am EST yesterday we noticed that one of these servers was performing poorly because it was receiving an unusually high volume of check-ins. Maybe there was an incredibly popular party that we missed out on! :)

Anyway, after trying various things to improve the performance of that server we decided to try to add another server to take some of the strain off the original overloaded server. We wanted to move this data in the background while the site remained up - however for some reason when we added the new server the entire site did go down. Ouch!

We tried all sorts of things to ease the strain but nothing seemed to work. By around 6:30pm EST (phew, what a day!) we decided to try one final idea, which fortunately worked. Yay!

However it took a further 5 hours to properlly test our fix, and so it was only by around 11:30pm EST that we were able to bring the site back up. Don't worry, all of your data remained safe at all times, and that hard-won mayorship is still yours!

...

Anyway, if people disagree that you should always communicate with your customer at a level they understand, then I'd urge you to read http://steveblank.com/2010/04/22/turning-on-your-reality-dis... or http://www.readwriteweb.com/start/2010/05/is-your-startup-to... (pitching to investors, media or customers - it's all the same issues).