From what I've read, CPU performance will be anywhere from a 3% - 10% improvement. The biggest leap will be in the iGPU, which is speculated to be 20% ± more capable. But Haswell is only speculated to released in June. There doesn't seem to be any official news on when it's slated.
If you're asking due to whether or not to purchase an Ivy Bridge system for the price drop, then that's entirely your call.
No, wait for Haswell. Since you are looking at laptops, haswell laptops are supposed to be able to run all day on one charge. Also, there is a special version of the Haswell that has doubled graphics horsepower that will be for laptops. The desktop Haswells will only have the 20% increase in GPU power.
That would only apply to the "ultra low power" versions of the mobile Haswell CPUs which consumes 10w. If it is going to be anything like the Ivy Bridge "Y" series, then clockspeed will be pretty low in comparison to other typical Haswell mobile CPUs. Additionally, the "Y" series has the lowest clocked Intel HD 4000.
I will speculate that the Haswell "Y" series CPUs will have a low clocked version of the Intel HD 4600 (GT2), not the Intel HD 5000 (GT3) which has been speculated to be up to 100% faster than the Intel HD 4000.
Waiting for Haswell is a good idea if long battery life is extremely important. However, gaming laptops will not have the "Y" series CPU. They will have Haswell CPUs that will consume 15w - 17w if looking at ultrabooks. The 25w - 35w dual Haswell CPUs will be found typical laptops including the average gaming laptop. The quad core i7 Haswell CPUs will probably range from 35w - 45w.
Other than the "ultra low" version, I don't really see a dramatic increase in battery life, because the difference in power consumption of "typical" mobile Haswell CPUs vs. Ivy Bridge CPUs will not be that much.
I'll need to do a bit more research on Haswell's mobile CPU power consumption to provide a better answer. But I think given the little information that I have read so far, my opinion regarding battery life seems reasonable.