Once upon a time, MobileMe was called ".Mac" (pronounced dot-mac). I bought this service for one year, and though it was cool having an exclusive email address like email@example.com, there wasn't much else that justified the $100 I paid. For one (then and now), the storage space was too minimal (you can get free space using DropBox that's the equivalent of MobileMe's paid space). For the same $100 a year, I have a business-level web hosting account with ixweb.
The real deal-breaker for me with MobileMe was the syncing between computers, which NEVER WORKED. My understanding is that it still doesn't work right. The iPhone now makes that irrelevant for me. If you don't have an iPhone then a normal cellular phone or Google probably makes that irrelevant for you too.
It's true that the Find My iPhone feature is tempting, but if Apple was smart about this, they'd recognize that most features they're selling with MobileMe are available free online. They should sell just the Find My iPhone and Back to My Mac features for a cheaper cost; they'd make more money. I'd subscribe for those features, if the price was right.
“Is a MobileMe subscription worth the money?”
Umm… It’s complicated.