Two major flaws for what is otherwise a really great idea. First, and what is just an odd omission is the lack of a built-in falsh. Even with a DSLR that can be very useful for the odd bit of fill-in flash, social occasions when you just want to tote around a separate flash gun, or where you suddenly find yourself confronted with such a circumstance where it would be useful yet it is not close too hand or would take too long to fit. Of course any such flash would no doubt increase the size of the body a bit and would be vulnerable to red-eye due to the proximity of the flash to the lens axis. However, you can generally fix those things later in post processing.
However, that "feature omission" is not the killer issue - the make or break deal on this sort of camera for those who will try an use it seriously is the speed of the AF system. Necessarily this is based on contrast detection systems, which are famously a lot slower than the phase-detect on SLRs. However, they are fundamentally more reliable being truly closed-loop. What matters is the speed as the sort of shutter lag seen on compacts is not acceptable for this type of camera. The Panasonic DMC-G1 proved that it was possible to produce performance approaching that of cheap DSLRs. Early reports on the Olympus are not so positive.
For many people, the Panasonic Lumix DMC-GH1 will be a better choice as it now includes the videos capability missing from the H1 and has a (sort of) semi-optical viewfinder and a flash gun.
What's required is something around the size of the Olympus but with built in flash and the AF performance of the Panasonic.