As promised, here are sample 720p/30fps HD videos taken using iPhone 4:
Play the video first. Then, once you see it on the playbar, click on resolution options and choose 720p.
Walking Around with Joshua Topolsky
Quoting ImRightWinger of Youtube:
colors are washed out and it blurs when moving due to the fact it has no stabilizer. [...]
Based on what I've seen in the videos, I agree. However, we have to keep in mind that this is actually a phone; And given that, I'm quite impressed.