I'm running wordpress v 2.7.1 which keeps prompting me to upgrade every other day to 2.7.1 (which I'm already running). If I install/upgrade a new plugin the message also reappears. If I click on the automatic upgrade it is quick to remind me I'mm already uptodate and the message goes away.
I don't really have a problem with it showing back up, its not like its this super glaring annoyance, but it does signal to me that there is something wrong with the automatic upgrade feature so someone may want to check this out.