Whoa! This message thread is from Oct/Nov of last year. It was brought back to life this week, and then BUMPED up by the same person.
Hello?
LOL I knew something was wrong as soon as I saw someone talking about still using MobileMe...
It seems to me part of the issue is people understanding what iCloud offers, which perhaps Apple should do a better job of highlighting/explaining.
On the Music front, If you have iTunes match anything thats matched to iTunes does not count against your storage space, as it just uses the iTunes store copy. Personally I have over 100gb of music, and iTunes match was able to make it so I only ended uploading about 1gb of music as it was able to match the rest. Unless you have a large amount of unusual music thats not in the iTunes Store you probably will not have to upload much.
On the Syncing front, I use my Corporate Exchange, Gmail (as Exchange - Email Only) and iCloud. I've never had it duplicate things on me or otherwise screw things up. I like having my Personal Calendar on iCloud and work on my corporate exchange, and they both show up on my phone so I don't overbook my self! iCloud also syncs things between iOS devices exchange and others cannot like notes.
At the end of the day iCloud is free, if you are unsure give it a try, you can always turn of the sections you don't use/like or just not use it at all.
Not sure if iCloud being enabled uses more battery, but I have no issues there as I have a plug at my Desk, home and Car if it gets low or I know I will be away from charging for extended period of time coming up I charge it up!