I've installed it twice - once as a new install, once as an upgrade to TB2.

New Install: Generally painless. It talks to the mail server and figures out what protocol to use automatically. For me, it defaulted to IMAP and once it did so I couldn't (and still can't) figure out how to change it to POP. However, IMAP works well and gives me a chance to play with it (I've never used IMAP seriously before, believe it or not).

On marking mail as "Junk", I have to actually move to the next message with the arrow key, or take the additional step to Delete it.

Upgrade Install of a POP Account: Painless. Kept my e-mail settings. It starts up and indexes all the existing mail. It shows 4 tabs, some of which give information about new features, caveats, etc.

On marking mail as "Junk", it works the way TB2 did - it moves it to the Junk folder and moves to the next message.

The Anti-Spam logic seems better than in TB2 (in TB2, just about every message with Viagra in the Sender gets through no matter how many times I mark it as Spam. In TB3 it seems to learn quicker.).

So far, so good.

If you're doing an upgrade of a POP account, it seems a no-brainer. If you're doing a new install, read-up on it if you want to use anything other than IMAP. (Note that I haven't yet upgraded an e-mail account that uses Kerberos-like authentication, so I can't comment on that yet.)

Cheers,
Scott.