In Mail I'm glad to be rid of the drawer, and I don't even mind the new icons, but you can't resize them any more (except for the mailbox icons). Why would Apple take away user choice in this matter?
My real complaint with Mail is that I had hoped that 2.0 would improve IMAP support, and it hasn't. Mail still doesn't recognize my IMAP Sent folder, so if I ask it to "leave sent messages on server," they just disappear into the ether, not being saved anywhere. Thunderbird and Entourage have no problems with this, so why can't Mail figure it out? (On the plus side, Mail finally handles "reply in format of the original" consistently, which I don't believe it ever has before. In all previous versions, it did not reply to RTF messages in RTF unless RTF was set as the default composition format.)
Also, Spotlight is not yet fully usable, as many people have pointed out. It's not fast enough (even on my iMac G5) to prevent the annoying phenomenon of reordering a search result just as I start to click on something, so that I end up clicking on something else. So I am sticking with Quicksilver to search for anything that QS can index. But when you really have to find something -- even in PDF! -- Spotlight is an invaluable timesaver.
Dashboard is obviously the replacement for Sherlock and/or Watson, so when more widgets come out to duplicate those functions -- eBay searches, phone book lookups (the Yellow Pages widget sucks), etc. -- it will be a terrific feature. But again it's not quite there.
It's a bummer that you can't use the Dictionary contextual menu in BBEdit or OmniWeb (to name just two), but that's not really Apple's fault. Still, I hope that feature can be incorporated into more programs, especially BBEdit.
Finally, printing with my old Epson is broken in Tiger. Major bummer.