I'm on 1680x1050, but I rarely (if ever) open windows beyond around 1024 wide, I just like having enough space to be able to see the other stuff I'm working on at any given time.
1400 x 1050 here, and I use all of it. Ubuntu sticks all my other opened stuff in little tabs on the bottom of my screen. I flip between tabs rather than having a lot of little windows (exception: when I'm using GIMP, I often have the toolbar on the left, and all the open images stacked on the right).
Prefer? for using on own PC? Use 1440*900 (or something close) as I have a widescreen laptop.... in this day and age of LCD screens which have a set resolution and if fed with something other than native they simply rescale do people really consider themselves having a choice any more or do most still not understand that what ever they select they actually get the same?
Well, 1280x1024 is what my monitor is made for.. so that's what I use, and I like it. What I prefer depends on what looks best on the screen.