Several years ago I signed up for a service called .Mac (dot Mac). My intention with .Mac was to have an @mac email address for life, have a place to back up important files, and to have a way to sync bookmark/address book/calendar data with several computers. You know what? It did all of those things really, really well. Sure there were outages, but they never really affected me since none of my uses were mission critical.
The day the iPhone was announced (Macworld, January 2007) I was extremely excited at the prospect of over the air (OTA) syncing with my iPhone. Push email on the iPhone wasn't really of interest to me, mostly because I never understood the advantages (I still don't get it). Regardless, OTA syncing with .Mac was never to be.
Then the world brightened. MobileMe, the renamed an much improved .Mac offers everything .Mac did, but so, so much more. Now when I add a date to iCal, it shows up on my iPhone automatically. Am I bothered fact that it isn't instant? Not in the slightest. What it means is that the next time I add an event on my phone, it will automatically show up in my iCal on my Mac, and at MobileMe.com. I don't have to plug my iPhone into my computer. Neat.
My address book is also in sync, as are my bookmarks across my iPhone, my laptop (MacBook Pro), and my desktop (a pc running Windows XP).
Remember just three years ago how horrible the land of data syncing was? I don't have to think about this syncing stuff anymore.
MobileMe is everything I need, and it works flawlessly.