Human eyes see things better in widescreen. Looking at my 17" 16:10 iMac, there is room for another one next to it, with very little movement from me to see it. That said, I don't like losing too much vertical space either.
I'd say...
For displays < 24" (or there abouts), 16:10 is nice
For displays ≥ 24", 16:9 would probably be better in an ergonomic sense, and you still have plenty of vertical real estate.
I think all laptops should stay with 16:10. Both because of the vertical issue (but this depends on resolution, and the 15.4" may go to 16.1" in 16:9 to reduce the loss). The other reason is the greater choice of monitors in 16:10 at the moment. For example, I'd like a monitor with DVI for my mac and HDMI for PS3 that throughputs HDMI audio to its internal speakers (or sound output) AND has a 4 port USB hub. The only monitor I've seen with that is the Dell SP2208WFP, which is 16:10. That space would be wasted if both my mac and PS3 are 16:9, yet I haven't seen a 16:9 version of this monitor. (But I'd be lying if I said I'd extensively looked. 😀)
As for 4:3, that's long gone. Too rectangular. While you could argue that it's suitable for any screen less than 12 inches, it's just not a widespread ratio anymore. 0% chance that the new laptops are 4:3.