The thing I like most about the nub is the degree to which it is integrated with the keyboard. Given my normal "ten finger hunt and peck" typing style, I found it very natural to intergate key&pointer operation.
Just my sticking up for the little nub, I would use my ibm to play games, i like it that much, but the pentium 90 can not hang
Laclasse, I think if you used the mx500 you might actually like the buttons. I find them to be great when mapped to a useful function(ie. enter-thumblarge, alt-f4 -thumbsmall). You would be suprised how much faster you can be at windows with an enter key. In case anyone tries these settings, remember that the logitech drivers are garbage. the alt-f4 button is my bane right now, but the intellipoint drivers with intellimouse explorer are golden.