So I went out and got me one of these. T Mobile, 1200 mins, 500 texts, unlimited Internet (< fucking win)
I've switched from my much loved iPhone 3G S and the first thing I noticed was the sensitivity. I wouldn't call the Samsung unresponsive, far from it, but the iPhone just edges it in it's "feel" of the touch screen. I don't think any smart phone can get close to the iPhone, but the Samsung does a good job.
The AMOLED screen is astonishing. I downloaded a few hd wallpapers and was bowled over by how crystal clear and bright it was. Makes the iPhone look very dull and low quality.
The Internet is fast, real fast. Using just a strong signal, it can give the iPhone a run for its money using Wi-fi. With the Wi-fi it's only marginally slower than my computer using google chrome.
It's so light, it's actually strange at first holding it. The iPhone has a comforting weight to it, but the Samsung does away with that to give it a really crisp feel. Combine the low weight with that massive screen and it's a brilliant phone to whip out if you want to show off in the smart phone pissing contest.
It will take some getting used to, it feels much different to my iphone, and I'm only just starting to scratch the surface of what the phone can do, but early impressions are very, very good.