Short and simple, GfxBoost activates “QTV” mode for specific surfaces. This makes for example DirectDraw display smoother and: a bit slower or significantly faster, depending on how you look at it. It also seems to have a small effect on Direct3D/OpenGL.
For HTC-built MSM7K-based devices only! All MSM7K are technically capable, but only HTC’s may have the correct drivers. Will probably not work on stock ROMs.