they do a nice job of pulling some of this stuff together in a way that is fully integrated and less kludgy than other options. Some of us like to just drag our photos in iPhoto to a folder and poof...web gallery. Instantaneously linked to relatives and to my AppleTV. Add to that the ability to do the same from the iPhone with MobileMe. 20GB storage. Decent email product. syncing devices via push across different platforms, including ability to align windows outlook to iphone, mac computers for calendar, mail, contacts. iDisk. All executed elegantly. For a $100 a year? works for me. Not that other solutions aren't also good, but to me.. this optimizes the value of being on a Mac in the first place.
If i was an exclusively PC user who owns an iPhone? nah, I wouldn't use MobileMe. granted i would shoot myself for being exclusively a PC user.