I like the GH-1 spring loaded battery and SD card slot covers. The E-P1 cover has no spring.
I like the E-P1 battery/card cover latch because it latched automatically. The GH-1 battery cover does not self-latch.
But the GH-1 battery cover has a catch I can work with my thumb, the E-P1 catch I have to fiddle with my thumbnail to open it.
I dislike both battery compartments, or the batteries, because there's no clear indication which way the battery should go, and it fits either way. Except on the Olympus if it's the wrong way it stops after a few millimetres and won't go in, but the Panasonic goes all the way in and then falls out again.
I wish I could have the best features of both cameras on both cameras