i've been using dual monitors on my g400 for almost 2 years now...i can't live w/out them! i drag aol, icq, MIRC, winamp, EVERYTHING over to the right screen, and leave my main larger screen open for web browsing, writing in word, etc.
i've also found it invaluable if you are writing stuff and want to quote web pages or whatever...just open the web page in the right screen and full screen it and open your word document in the left screen and full screen it and start typing like crazy! SOOOOO many uses.
one tip would be to play with refresh rates if you find the monitors interfere with each other..or separate them by more than you thought you would. i occasionally get scan lines due to interference, but it's really not noticeable at all.