It wasn’t two weeks between 2.8 and 2.81. It seems a few things broke.
WordPress 2.8.1 fixes many bugs and tightens security for plugin administration pages. Core Security Technologies notified us that admin pages added by certain plugins could be viewed by unprivileged users, resulting in information being leaked. Not all plugins are vulnerable to this problem, but we advise upgrading to 2.8.1 to be safe.
We always try to wait a few days after a release to upgrade sites, just in case things break. The other issue is that plugins that you need may break. Always backup completely before doing an update to save yourself some headaches.