Before I saw the episodes I thought 10 was plenty, but now I think 12 might have been a better idea just to let some scenes breathe a bit better.
To give a flavour of what scenes have been cut (spoilers obviously):
Robb and Joffrey trying to have a fight and Rodrik stopping it and Sandor insulting him, also the Bran/Tommen mock duel beforehand. This was filmed for the pilot, but I don't know if it was reshot. Hopefully it'll resurface on DVD. Also Barristan and Renly meeting the royal party and being charmed by Sansa; now only Ilyn Payne shows up.
So fairly minor in the grand scheme of things, but some nice little character moments anyway.