Half a dozen or so running applications, with probably 20 or 30 windows. The big problem went away with the advent of tabbed browsing and IRC :-)
Screen is 1280x1024.
If I'm "developing"[0] one of my Awful Perl Programs, then this goes up by about 10 or so (perl module, perl program, source data, source data, output, perl documentation 1, google window, run window, debugger)
It's far, far faster for me to whack F9 and grab the window I want than it is for me to footle around with multiple desktops; all they do is provide me with a mechanism for losing windows.