The 15" Flexview was the best of all of them, but I am not suited to SXGA+ and it was larger than I wanted. I did find the display, although it had decent viewing angles, to be very subdued and soft.
Unless you have eye problems, I think you
are well suited to SXGA+. It's something you have to get used to after XGA, but things aren't so tiny as to present a usability problem, as can happen with UXGA, and you can get a lot more on the screen. I think every new machine you buy will force a period of adjustment, after which you'll be completely at home-- unless there is a real problem. I'm just saying that for the great bulk of people out there, it's not a problem.
My girlfriend has a 12" XGA Inspiron 300m. At first I couldn't stand the size/resolution, but I got to like it pretty well, although I wouldn't go much smaller than that with XGA.
I have an Inspiron 8200 with an UltraSharp 15" UXGA display. The display on
that machine is beautiful: sharp and evenly lit, with great color and decent response time. Overall, it's a better monitor for displaying images than my 2001FP 20" LCD monitor. However, the resolution at that size winds up being annoying. I would never even come
close to getting another 15" UXGA screen.
I know what you mean about "subdued and soft" with the FlexView displays. At first I wanted to make mine impossibly bright, but after a few days I really got used to it, and found that it seems to reduce eye strain. I'm not an IBM lover, either-- I'm forced to live with this machine from work, and I'm just finding that I like it. Some bonehead mistakes were made with the keyboard (for instance, the lower-left key is the FN key instead of CTRL-- most Thinkpads seem to be like that), and the touchpad isn't optimally designed, but I'm mostly liking the laptop.