If you take full advantage, .Mac is worth the money. I'd still like to see more space given and larger attachments for mail, but the iSync is great, being able to use my bookmarks and acccess my files, even at work and even on a Windoze XP machine, is also well worth it.
As well as having a quick and painless way to have photos and videos for the family to see in one area and a place for my clips and c/v and design work in another. And having a @mac.com e-mail is also nice.
Not to mention the free stuff that comes down the pike here and there.