Battery performance using bluetooth does go down quicker, but not a crippling amount. Most I would see using their phone as their pc is an hour or two. I haven't needed to use it for work yet, just tested it out with my iMac's bt keyboard and magic mouse to ensure everything worked as advertised. And there is no hit in performance. Remember this phone has a very fast cpu and 2gb of RAM. It's hard to tax this phone. Even playing games like Modern Combat or NOVA3, which are very graphic intensive, don't phase the phone.
As for expandable storage, I am referring to sd cards. Online storage is okay if you have a fast and solid wifi or lte connection, but you are required to have that for online storage to work. Having a connection isn't always possible. As for the sd cards, I have a couple of 32gb ones, which are less than $30 a pop, so I can change them in andout as I see fit. One for work and one for play.
And of course, I forgot about the video overlay feature. I can watch a video, while still working on a document or playing a game, or texting. I love that pop-up feature. Good for diy projects.
Stock feature wise the S3 provides what only a jailbroken iPhone can, like changing the look of the phone via a launcher (same as Dreamboard in Cydia), access to all of your files (like iFile), attaching any type of file to an outgoing email (like the mail attach tweak in Cydia), etc... It is a long list of stuff. For me, the advantages are clear and make my life easier. I still have my iPad2, but always trying to figure out work around or opening multiple apps to do one thing is just a pain. It has come down to personal preference for me, for which I choose Android. I'm still waiting for iOS6 though to see all the features it has. And no matter what, my household will always have an iphone in it, because my wife only wants that phone and prefers iOS to Android.
Anyway, Here is a long video you can skip through to give you an idea of exactly what I am referring to. I haven't even done some of thethings this guy did:
http://www.youtube.com/watch?v=46IiRyigUH0