I went to compose a new message in my .Mac webmail recently and found a new icon: Spell Check. In .Mac Mail's preferences are a number of language dicationaries to choose from but no custom dictionaries. Also, prefs has a checkbox to enable auto spell check when sending.
While in Preferences, I also found an Email Aliases feature under the Accounts tab. Pretty cool. Set one up for myself. I can give that alias when signing up for stuff when I suspect they might sell my address. I could also create an alias that I give to just friends/family. Great feature.
Looks like new .Mac account features rumored elsewhere for later release are starting to trickle in.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040624153303475