Xbox360FanBoy post an article that takes a look at that bain of Live ID where if your gamertag is saddled with a Hotmail or MSN email address, your link between the two is unbreakable. Discovered long ago, it is impossible to associate your gamertag with a new email address if your Windows Live ID was automatically created by a Microsoft site like Hotmail or MSN. Before, it was a minor annoyance, as it forced many to maintain an email address they had long since abandoned. Now, with the release of Live Messenger integration on the 360, it's become a serious nuisance.
Major Nelson posted a quick FAQ about the update specifically mentioning this problem. According to him, a future release (sooner than the Fall Update we hope) should allow anyone to change the email address associated with their gamertag. The sooner the better, because Xbox360FanBoy is sure there are thousands of unfortunate souls ready to put their Hotmail addresses to pasture (where they can frolic and collect spam).