As has been reported elsewhere, Mail 2.0 in MacOS 10.4 is pretty different. I thought I'd share what I like and don't like about the update to what I still believe is the best email client in existence.
Before I start, you might be wondering why I think Mail is teh best email client. My old TiBook 800 has been dying for the last month (overheating bad--I can't figure it out), so I started looking for a replacement because I've been doing all of my email, instant messaging, and latex authoring on my mac. I seriously considered not replacing it at all and moving all of these tools to my desktop PC, but after evaluating tools for email on Windows I just couldn't do it. Outlook, Thunderbird and Eudora suck, and there's no way I was going back to Pine, XEmacs or mh. Outlook is slow. Thunderbird has some serious glitches with the way it handles multiple accounts. All of them look nasty, and all of them have very strange behavior when you try to edit a quote-reply. I've used a dozen email clients over the years, and I've grown to love MacOS Mail. I thought about for a long time and decided to replace my TiBook with a 12" G4 mainly because I couldn't live w/out Mail, Adium and TexShop. If these programs were available on PC I'd have no problem paying $100, $50 and $50 for each of them respectively.
Conversation/Thread view is nice. It's snappier than Outlook and the color coding makes it easier to discern threads at a glance.
I think Apple is starting to understand "teh snappy". Mail 2.0 is more responsive. It looks like they finally put some multi-threading into the mail checks; previous versions would block on certain mail i/o and I'd have to force quit if my internet connection went down during one of these operations.
Spotlight integration is great. Searching mail is super-fast and intuitive. It's required a little retraining for me to get used to using Spotlight, but so far it's been very useful. Spotlight isn't a new idea, but I think Apple's done it a bit better than previous incarnations for 10.3.
Junk mail filtering feels a bit smarter. It seems to be learning a lot faster than my previous Mail on 10.3.
Yeah, it's ugly. I'm a little flabbergasted that the Mail designers broke the UI guidelines repeatedly in Mail. Of course, this is usually the way Apple works internally: some renegade team with Steve's blessing makes some gross UI violation, and then a year or so later it shows up in the official UI guideline document as a sanctioned way to do things. Quicktime, iTunes, Safari, the "brushed metal" look, etc., now Mail.
The drawer is gone! You can still make the mailbox view go away (Cmd-Shift-M), but it can only be shown on the left. I liked it on the right better. I actually think showing the mailbox hierarchy on the left is a poor UI decision. Westerners read from left to right, so important, frequently accessed information should start in the upper-left corner. I liked keeping the mailbox view on the right because I didn't access it that much. At the very least they should have designed it so you could move it to the right side if you wanted too. With the drawer you could do that.
What happened to the status bar? I'm a geek, I want to know what's going on at all times! Maybe there's an option somewhere to get it to reappear, but I'm not finding it...
I'm a little disapointed that IMAPS still isn't a first class citizen in Mail. You can enable IMAPS for a server, but only after you've added the server as an IMAP server first. If your mail server rejects IMAP connections it can be a little awkward getting the server added to Mail.