Back when I worked at Apple, we all got a free .Mac account. This was so we could create our own sites and demo some of the features using our personal accounts. Got switched over to MobileMe when it changed and I've since renewed.
I don't have a Mac yet either, but I'll share with you some of the things I love.
Email, Contacts & Calendar - Synchronized across my computer, my iPhone and the Web.
Setup is so easy - 1 user name, 1 password.
iDisk Backup - I use GoodSync for Windows. It's set up to automatically back up my documents, photos and music to my iDisk.
iDisk access on iPhone - Always have access to my files that are backed up to my iDisk (using Quickword + Quickoffice Files)
The other thing that I'm going to love is that when I finally get a mac, I don't have to worry about email, contacts and calendars. I'm going to enter my Mobile Me email address and that stuff will start syncing. (Don't think it does this during the setup assistant, but it would be awesome if it did).
My one gripe is that MobileMe doesn't sync bookmarks with Firefox.