I saw one today at the Apple store.
Impressions:
1. The extra real estate is incredible. I did some side by side comparisons, and it really is 23" inches of real estate.
2. It's nice. One thing I read is that this new display has the highest PPI of any display Apple makes...even a lot more than the 30". You can tell when you look at the screen.
3. Until Leopard, things are a bit tight on the UI. I was worried things would be too small. For my eyes, I thought it was small but doable. I would only worry about eye strain over time.
4. To that point, if things are too small, you can set it to the old resolution is you really want. to..
NET/NET: Even though I own the last generation MPB 17" which is less than 8 months old, I bought the new model today. Not a major update, but that screen was compelling enough to warrant the money. (Or so I hope.)