WordPress has announced that on Sunday, 15 February 2009 at 20:00 GMT (noon PST), WordPress.com bloggers will be logged out from the system for a short while as the WordPress.com team is busy making some code changes for maintenance.
So what is the problem? Unsaved WordPress Work will be lost during this period as you will be logged out. So they advise saving your work shortly before the maintenance begins just to be safe.
Do you need to back up your data? Not required and they assure all bloggers that the data will be safe.
Does it affect self hosted WordPress blogs? No. Its under your control.
There is no downtime associated with the “maintenance” We just have to make some changes to the cookies we use to determine if you are logged in our out. These changes are a result of the 2.7 upgrade a few months ago and upgrading WP.com to PHP 5. We have been putting it off for a while now.
The only side-effect is that you will get logged out of WP.com and will have to re-login (as I mentioned in the notice). There are no user-facing changes that come along with this. Normally it is not something we would announce, but the fact that if you are in the middle of composing a post, there is a risk you will lose 2 minutes of data (since it auto-saves every 2 minutes), we figured it would be worth giving folks the heads up. Also, some people may be confused by the fact they have to login again since normally their browser “remembers” them as being logged in.