I have been playing around with the demo version for a while now and here are my likes/dislikes:

Likes:
1) Better control over mpeg2 rendering (variable bit rate, 2-pass, etc.)
2) Key framing effects (no need to split your video or stills into little chunks to apply multiple pan/zoom effects, etc.)
3) As you mentioned, the unlimited video/audio tracks.
4) Many more video effects, transistions, etc.
5) Although I can't access it in the demo version of Vegas 5, it has AC3 surround sound.
6) Has the same basic look and feel as MS 3 and 4, although some of the layout is a bit different.

Dislikes:
1) In MS 3 and 4, when you brought up an effects window, it had its own play / stop buttons so you could view your effects. In Vegas 5, I could not find such a button. I would have to keep moving the window to get to the play buttons near the time line.
2) Much more expensive than MS 3 and 4. I will have to wait a while to purchase a copy.
3) This is probably due to the fact that I am more comfortable with MS 3 and 4, but I found things a bit harder to find in Vegas 5. If I had started in Vegas 5, then tried using MS 3 or 4, I would probably feel the same way about the new software.

Although I have played with Vegas 5 for only a few weeks, I will sorely miss it when the demo period expires. It will take quite a while for me to save up the money required to purchase it, but it is definitely worth saving for. I have kept an eye out on eBay, but there are no great deals there for Vegas 5 (darn it all anyway).

Hope this helps...
Al

My input, just some features that i think is awesome :)
1. Track control & motion
2. keyframes
3. velocity envelopes
4. dockable windows
5. beizer mask
6. 3D & compositing modes

To ADinelt : For dislike no.1 - try options - customize toolbar - add the play, stop, pause buttons - hope that minus 1 dislike ;) also, there's an upgrade price for VMS to Vegas 5 for 399.95

HTH