I have the i6000d with the x300 128meg card. I play wow at 1920x1200 with max settings. I get around 21-29ffps depending on where I am at in the game and how lagged the server is. Early morning times I get a nice 28-29fps since the server load is not that bad. The game play is really nice and I have not really used my desktop system to play wow at all since I got the 6000d.
I play HL2 at 1024x768 with the default hl2 settings with no issues. RoN plays really nice maxed out and so does civ3. I have not tried Warcraft3 since I have been playing WoW. Other than that I have not seen anything to make me not like the x300 besides it being a lightweight card in general. I am a meat and potatoes kinda guy, but I love my battery life more. So until I can fit a cold fusion reactor into my laptop and it not exceed 8 lbs I will be happy with the x300 cause it does the job and it does it well!