Microsoft are claiming 50% graphics improvement (officially) with the HD 4400. Many people say that the improvement will not be that high however they missed a small key point. If you watch the SP2 MS announcement you will hear Panos talking about the SP2 now having dual channel memory (SP1 has single channel). This means the CPU will have almost double the bandwidth at it's disposal. This also applies to the HD 4400 since it's integrated.
And here's one of the first reviews!
Microsoft Surface Pro 2 review: a tablet that works best as a laptop
The SP2 is smashing competition in performance and according to the benchmarks the 3DMark11 score has almost doubled compared with SP1.
LOL to all the people who said "the benchmarks will be the same as every other Haswell laptop"
I can't wait to crank DOTA 2 on this thing tomorrow.
*\cream pants*