It's running so much better than I expected on my 4S. There's a few stutters here or there when activating spotlight, and there's some bugs, of course, but nothing that makes me want to drop everything and reinstall iOS 6. I feel like Apple is developing iOS 7 rather well to be on Beta 4 and be this close to a great-running OS. It's also doing great on my mother's 4. Although, I truly am curious how it could've fared on my father's 3GS.