I just tested out seven different mics into my GH2. I tried to get a cross-sampling of all of the mics out there, from a $35 Audio Technica mic, all the way up to the $1249 Sennheiser MKH 8060. Here's a link to the article & video:
Most of the video was shot with the regular GH2 firmware (and the 20mm Lumix G lens), but the very last shot was done with the GH2vk hack, using the cbrandin's 66mb patch. I hope you find it helpful!