Both Panasonic and Olympus have been hyping on their "fastest in the world" AF system like teenagers with inferiority complex. Why do I say that? One of the main concerns about mirrorless systems (vs. DSLR) is the AF system. CDAF is associated with slowness because of its use in PnS cameras and Live View modes (which are slow as snails on DSLRs). And for many years that was true. It was only recently with the release of the E-P3 and GH-2 that the situation changed.
That said, under tough conditions, both CDAF and PDAF will fail to acquire focus. Surprisingly, that is where m4/3 actually shines: you can get a magnified view in the EVF to aid MF. You have to rely on the LCD screen for DSLRs, which is unwieldy to say the least, especially if your camera and lens are heavy (60D + 15-85 is already over 1kg. Imagine 5D Mk III and 70-200 f/2.8L!)