Lots of folks have been sending me e-mail or asking on IRC, "So, what's new in Mozilla 1.5?" While I haven't put together the changelog for the 1.5 final dev cycle (we've fixed about 55 bugs since beta and I expect we'll fix a dozen or so more before release) I have finished the Mozilla 1.5 Alpha changelog and the Mozilla 1.5 Beta changelog.
A quick glance at those two lists will give you an idea about the roughly 1000 bugs squashed and features implemented during the 1.5 alpha and beta cycles. The lists aren't perfect because they're just pulled from Bonsai and Bugzilla queries, but if you want to know what's new in 1.5, it's probably the best place to start.