From http://www.notmacchallenge.com/ :
Since Apple decided to start charging for dotMac, I’ve spent $495 to keep some useful files remotely accessible on my iDisk and sync my bookmarks, address book and calendar between computers. While I find these features incredibly useful and convenient, I have no need for any of dotMac’s web-based services, and as a result, I don’t think I’ve been getting a good value from Apple. I know that workarounds exist that allow one to take advantage of dotMac’s services without a dotMac account, but they require a level of technical proficiency that I just don’t have. I’ve no doubt there are a lot of people like me.
I wish them the best of luck, however, the requirements are a bit weird. Mainly, it appears that this is to work in conjunction with .Mac, not replace it, which is a far easier and more laudable goal, IMO.
