Touchwiz is more than just a "launcher." It's a complete UI overlay...and it's ugly, and it's laggy. Maybe I didn't get the same phone everyone else did, no? Touchwiz launcher itself is clumsy and slow, and I personally think it's terrible. I don't know where you people getting off saying it's the best launcher you've ever used. Have you tried them all?
And yes Touchwiz4 was by far the fastest launcher of them all (especially on the SGS2) ,maybe SPB and TSF came close in terms of smoothness but I didn't like them.
As for looks and functionality ,it's not that ugly but can become boring after a while ,on the S2 I had go launcher ex as my primary launcher, but on the note I'm actually still on touchwiz.
I don't know why your experience differs from ours , but what I just told you is from personal experience with two different devices , SGS2 (6 months till I sold it ) and SG-note (3 weeks now ) .