my friend got this phone (Galaxy S) and here are my initial impressions:
1) The display is truly stunning. my Legend looked like an el-cheapo ass before GS. From normal text to movie playback, thd display is worth a thousand tech salutes! Its the greatest thing in this phone. Nothing can come close.
2) touchwiz 3.0 still has long way to catch up with SenseUI. It still is confusing like hell, not many good widgets.
3) the build quality is damn good. It's totally lightweight and thin. easily pocketable and one handed operation is very easy to do
4) Samsung Kies sucks. my friend came to my place. Phone is not connecting to windows 7 or ubuntu in mass storage mode. It just doesn' have this option. Will report back on this in two days.
5) Touch sensitivity is really high and finally, I think there is a phone whose touch response matches that of iphone.
6) music quality is similar to what I get on Legend. Though not as refined and clean as that on ipod touch, it's decent (I didn't like mids and highs that much)
7) bundled earphones are great (as per my friend). comes with in-ear headphones
8) it's damn fast. But when I started copying 280 files form SD card to phone storage, the phone came down to a crawl. everything became super slow.
9) you cannot do anything when the phone is connected to PC for data copy or sync. Unlike Legend, you have to leave the phone alone. And when you connect the phone to PC when some app is open, the phone rejects to sync. Damn you Samsung
10)
Finally, I am left with mixed emotions on this one

A lot of research needs to be done on the phone still. Will give a more and clear update by this weekend.
Those who are moving from symbian or plain android or any other UI that doesn't have SenseUI will find the UI really appealing but those who are moving from phones like Legend or Hero with Sense UI will feel that something is missing.