I've been slowly, slowly moving everything away before the subscription expires on my account. I've been a MM subscriber for about two years and it's "ok" but nothing spectacuular... I wouldn't say it's overpriced, but there is some inherit mediocrity in some things. Mail, for instance, doesn't have server-side filtering and the webmail function is dog slow if you have a lot of mail. iDisk is integrated right into the OS but can be finicky (ie. Error -14, or random "iDisk not in sync" errors) and is not SSL secured.
I switched my e-mail, calendar, and contacts back to Yahoo, and use Dropbox for cloud storage.
Dropbox is f***ing awesome. I've been using it for the past few weeks and it I think it is a lot better than iDisk. LAN Sync is the real iDisk killer for me b/c I keep all of my crud on there, and don't have to wait for it to sync up/down from the cloud, but straight across to all my other Macs. SSL is nice, too.
Push e-mail is already done through Yahoo. Calendaring doesn't do Push but has full CalDAV access via the iPhone so it syncs up right away any time I open it. Contacts is the only thing that is missing but I don't update my contacts all that often to start with so it doesn't affect me on a daily basis like e-mail or calendar does.
I haven't really missed bookmark sync--it's nice to have still but not anything I've cried over. You guys would probably laugh but I actually use the bookmarks thing on my yahoo homepage for some stuff.
Other than that, the only thing I miss from my MM account is the Back to My Mac and the Find My iPhone which were both nice to have but I'm still debating if they are worth $99/yr (or $70 through Amazon).
If you'd like a Dropbox referral, PM me.