When I'm logging in to Unity in 11.10 it takes about 15-20 seconds for the Desktop to be ready. When I compare that to the loading times of 10.04 where it's almost instant there is a huge discrapancy in log in times. Is gnome3/Unity really that massive to not be loaded faster?
Please no unnecessary comments about:
autostart applications as I set none (at least not by autostart option via cog).
bootup-manager as I reduced the processes there to a minimum
15-20 seconds sounds about right, i got that sort of time when i was using 11.10, since i upgraded to 12.04 (being released tomorrow as of this writing), my login times and boot times have been cut down by about 60%.
In answer to your question, 15-20 seconds is not unusual at all for your hardware, my hardware is comparable to yours but with better graphics.