I recently got one for doing Apple's sales programme and I must say, I find myself using it more than I had expected. Here's my roundup:
-The mail is ok - nothing special... easy to set up multiple aliases is cool, but not overwhelming.
-iCards are a nice way to send e-cards without sending people annoying links to ad-filled sites that they never open anyway (iCards are sent completely - not just linked), but this is ultimately just a bonus.
-Homepage & iDisk is quite cool to get stuff online quickly. Lets say I just saw something that I find interesting at home - I can quickly drag it to my iDisk folder. Now let's assume I'm at another computer: Not only can I access that file, I can also use the .mac web interface to publish it to my homepage or an entirely new page.
The iPhoto integration is also really nice.
It is also a lot faster than most other WebDAV services I have used, although those were mostly free ones...
So if you aren't really interested in having a "proper" website hosting plan, .mac is a cool quick alternative to help you get stuff online quickly.
There's nothing here you can't do for free as well though - but chances are that it's such a hassle that you end up not bothering.