As many of 'em said (like led_shankar , the deconstructionist) it all depends on your NEEDS.
if its laptop you can do more work (coz u can take it anywhere),& if its desktop you can do work only where it is.
well i've got both of 'em, when i'm on the move,(travelling), at that time i can do a lot of work, checking mail, etc,etc & if i'm bored i can play games (Colin McRae 04, F1....).
& when i'm home i can do the work comfortably, & i get to play these games at a higher gfx. settings.