From benchmarking the Intel GMA HD, I have noticed a performance related "bug/flaw" which might affect it in real games.
Intel Core i5 661
Intel DH55HC BIOS version 028
2x2GB Corsair XMS3 DDR3-1600 C9 @ DDR3-1333 9-9-9-24
Graphics Media Accelerator HD
Intel X25-M(OS+Game Drive) G1 80GB 8820 firmware
Seagate 7200RPM 160GB(Storage Drive)
Windows 7 64-bit
Using the 3DMark2006 Professional Edition 1.1.0, on the SM 2.0 Graphics Test titled "Firefly Forest", you can watch the frames fluctuate rather greatly over the course of the benchmark. It goes from low as 1 fps to high as 9-10 fps, and it just goes like that. 1,3,9, 2,4,8, just like a counter in a different increment.
I have tested the CD drivers(184.108.40.2065), 220.127.116.115 and finally, the latest drivers, 18.104.22.1680. They ALL exhibit the problem.
There is a possibility this "bug" might exist in other code and games as well, although this is the only app I noticed with significant performance fluctuations. It would be very good for Intel to look into this.
This does not seem to occur with "Software Vertex Processing" enabled in the Graphics Control Panel.