iCloud has other functions than syncing iWork documents, most of which work very well. Syncing contacts, calendar and bookmarks among iOS devices and Mac works wonderfully, and is so convenient, I just love it. And iCloud backup of iOS devices is a real life saver. But as far as iWork syncing is concerned, they kinda dropped the ball there. Although if you read their promotional material VERY carefully, it says you can sync documents among iOS devices, and manages to leave out mentioning the Mac, but it's done so subtly most people will miss it unless they are looking for it. Anyway, I don't think there is any technical reason why you couldn't jump from SL to ML, let's hope Apple does right by its customers and allows a straight upgrade.
I beg to differ on bookmarks syncing well - unless you consider making hundreds of copies of the same bookmarks over and over again working well...