With any major new version of software, there are new bugs, and Tiger is no exception. A thread on MacRumors forums contains a listing of bugs reported from Tiger users. So far, there are some annoyances and glitches, but no major widespread show-stopping bugs (e.g. wiped firewire drives).

Regardless, our advice stands; unless you are willing to put up with some bugs and are surviving just fine with Panther, wait until 10.4.1 or later comes out.