I just loaded the D3 client on my wife's laptop and ran through Tristram and the Cathedral to see how well the game would fare and I'm happy to report that the game actually ran very well. My setting were:
Resolution: 1600x900 16:9 WS
Keep in mind this was not the actual beta and performance in the actual beta (and retail version) will most likely be slightly lower, but I'd say you are probably looking at decent medium settings. The Intel Graphics 3000 is comparable to the Nvidia 310M and the Radeon Mobility HD5450 both of which show "low" for performance on the Graphics Card List for D3. Anyway I was happy to see it run as well as it did since my wife uses her laptop far more than her desktop and we can for sure play the game together (Well technically she could use her desktop machine but this will work great.)
Tonight, I will run FRAPS and see what kind of framerates I'm getting on the laptop. It seemed totally playable to me, but actual numbers will help give others an idea of what to expect.