If you are not interested in the other features of MobileMe, I would stick with Dropbox. 2 GB is free and can get 50 GB/year for $99. Same price as MobileMe.
Thing is, MobileMe offers a whole lot more than Dropbox. Dropbox is amazing at what it does and I think everyone would agree since it is extremely easy to use multiplatform it is easier to use.
My only problem with dropbox is that you cant not save files into it from pages on the iPad. Other than that, it is the perfect way to sync your data.
Live Mesh by Microsoft is very good I must say. Despite the lack of consistency in its products (Microsoft has 3 sync features / clouds not connected with each other!), Microsoft made a good job with Live Mesh for Mac. Unlike Dropbox, you can choose folders that you want to sync and it will keep monitoring them.
A couple of months ago Dropbox 1.0 was released with support for selective syncing. You can choose the folders you want to sync on your computer.
I just installed it but I still don't see such possibility.
You can choose only folders that you want to sync from DB to your computer, but you can't choose the folders that you want to sync from your PC to DB...
Yes, that isn't possible.