I realize it seems like a lot, but thinking of it as the sum of all the services provided, I find it's a great deal. For my $99/ year, I get the following:
Personal Exchange server: Push email, contacts & calendar with computer, mobile and web access.
Remote wipe solution
Mobile handset locator
Low/zero-config remote access to my computer
Web Host
Photo gallery
20GB online storage/200GB data transfer
For me, it's well worth the $99. And even still, I know Amazon has it for way less.
Sure, if I wanted to, I could piece the same stuff together for less, perhaps free even, or get more for the same, but it's not integrated the same way.
Also, the only problem I have with the service is the fact that iDisk is really slow. Apple really needs to fix this.