Is there any reason to switch from MobileMe to iCloud if i'm still on Snow Leopard?
With Snow Leopard, you cannot Sync Docs, you can work around to sync Calendars and Contacts.

I would stick with MobileMe as you have the iDisk.

iOS5 and iCloud does sync docs accross devioces every time you make an edit. But sadly for me (Snow Leopard) I cant sync Docs to my Mac without first uploading from a device to iWork.com which is a bit of a shoddy work arround.