My husband's another one who's had it since it was free. I started a trial earlier this summer when one of my favorite iPad apps added iDisk support for backups--and they don't offer an easy Dropbox solution, so that's not a viable alternative.
Personally, I HATE syncing my iDevices the normal way, because I simply don't get around to it often enough, so it takes forever when I do. MobileMe means that for certain critical things such as mail, calendars, and contacts, I can "set it and forget it", knowing that what's on my iPhone will be the same as the MBP and the iPad. If I add a contact on the phone, I don't have to remember to go sync the phone with the Mac and then sync the iPad as well. It just happens, with no action needed on my part.
And again, if you have apps that support iDisk either as backups or additional cloud storage, the seamless functionality is awesome.
FindMyiPhone is just a big bonus. Like others have said, I end up using it within the house just to save time hunting the damn thing down. Send it a ping and it will make a piercing noise that's a lot clearer at a distance than any of my ringtones, won't stop sounding until I turn it off, and works even when the ringer is off. So yes, it does work better than just calling it!
We're switching to a family pack this week. $100 on Amazon, cheaper than Apple and half the price of two individual plans.