We have known for many months now that Haswell would offer substantially faster integrated graphics over Ivy Bridge, which was already a nice step-up from Sandy Bridge. According to Intel's marketing team, for at least the Windows-only 3DMark demo, Haswell can be in the range of 2~3x faster.
Intel also shared they will be marketing their higher-end graphics under the "Iris" product name. For what was known as Haswell GT1 will still be Intel HD graphics, Haswell GT2 graphics will carry a name of Intel HD 4600 / 4400 / 4200 graphics, Intel GT3 as Intel HD 5000, Intel GT3 28W as Intel Iris 5100, and Haswell GT3e as Intel Iris Pro 5200 graphics. It's the Intel Iris Pro 5200 model that bears the embedded DRAM (eDRAM) for really compelling performance.
From the Windows benchmarks published by Intel, it's on the desktop side where Haswell is closer to a 3x improvement over Ivy Bridge and 2x on the low-power mobile front.
Haswell hardware also supports OpenGL 4.0, OpenCL 1.2, and improvements to their video acceleration that's exposed via VA-API under Linux.
It will be interesting to see how the open-source Linux graphics performance is for Haswell, along with comparing the Linux vs. Windows performance, which you will be able to find next month on Phoronix as soon as the hardware launches.
There should be decent support for Intel Haswell processors in Ubuntu 13.04 and other newer Linux distributions while the best level of support is found in yet-to-be-released Mesa revisions and the very latest Linux kernel.