I have seen HD 3000 on a laptop play most games maxed out at 1280x720 (that also being a core i3), You wont be able to achieve enthusiast resolutions or settings, but most games will be playable, even at decent resolutions.
I will say though, a cheap Radeon card will give you much better performance.
My Lenovo IdeaPad Y470 has a Core i5-2410M CPU and nVidia GT 550M and 1366x768 resolution.
I tested the HD 3000 core with Crysis and Fallout 3. Crysis had to be set to low graphic settings and no anti aliasing (AA) to get between 18 FPS - 24 FPS most of the time. Switching AA to 2x resulted in frame rates of 8 FPS - 11 FPS. It was able to handle Fallout 3 better with graphic options set to medium (some tweaking is necessary to get the best performance though).
I suppose the HD 3000 can nearly max out Half-Life 2 since that is not a very demanding game. However, HL2 came out in late 2004.
SC2(low settings too, but this game is cpu limited for most things, I did not try any massive unit count user maps either) And Just Cause 2 Played. Just Cause 2 needed the lowest settings ever....and well, the fps was still low.
Source games worked better then I would have guessed for onboard. Not saying it is great. but for someone who will play old games or low system requirements games. it may just do the trick.