Problems? None here. Ive run the bleeding edge of Dapper for months with everything working just fine. Wasnt able to use Xnest for a few days, but its never used for much more than to show off.
Easy Ubuntu and Automatix, depending on version number, can do stupid stuff like change your /etc/apt/sources.list. Running them to install bits and bobs will in all liklihood never hurt anything, but with sh*tty sources, updating can be very fun indeed. Especially if you ignore advice and install a Hoary version on a Dapper box, do an "update" and all hell breaks loose.
Always back up your sources before running either is the lesson to be learned.
