So I am a Mac user. So I have an iPhone. And yes, I have a MobileMe account. I like MobileMe, but I don't love it. Why ? Well, it's simple and complicated.
By the way, I bought a MobileMe account before I was a Mac user (true story). I was planning to have both Mac and iPhone to improve my business, so I ordered a Me.com account while waiting for my Mac to be delivered. The first time I opened the interface, I thought it was a revolutionary mail client. And I was right because everything was easy, nice and ergonomic.
When I got the Mac and the iPhone, MobileMe looked like magic. There is not simpler way to synchronize everything on multiple devices (even what you don't need to sync).
But there is one thing that makes me angry against MobileMe : it is slow. Really slow.
Sending emails through imap is slower than with my other email accounts. Opening and browsing iDisk on the Mac is slow. The photo gallery is slow too (it takes a while to open a picture and fully render it).
I use my Me.com account as my personal email but I never open the web client. The iDisk is good to remotely backup important data. This is done automatically once a week but I can't do it more often because of the lack of speed. I use the photo gallery to share pictures with my family and friends, pictures I don't want to share publicly on Flickr even if it's not a matter of privacy. But I don't use this feature as much as I'd like to because the synchronization with iPhoto takes ages to be accomplished (even by direct upload via the web UI).
These days, Me.com is faster than before but it's still not enough.
Like everybody, I pay 79€ yearly for this. It is expensive for a service I only use 50% of the capabilities. But I still like it. That's weird...