You can always keep the camera in AF-S mode (switch top left on camera) then switch off the continuous AF in the movie menu. During shooting use shutter or touch-screen AF when you need to refocus. That's how I do it. Focus will then stay where you left it until you do either of the above things to refocus.
Or you could do half-pressing on shutter to lock the focus. AF works sometimes. But sometimes it just can't get it what I want. I like AF-C for deep DOF. I would definitely prefer MF + peaking for shallow DOF.
After using the GH2 on a real movie shoot over the last week, I'd say that the one thing that seems more useful than pretty much anything else is the ability to use the touch-zoom focus assist while an HDMI output is happening. I can't tell you how many times I pulled the HDMI cable out so I could use that feature, only to have to wait for a while for the HDMI to sync back up.
I didn't really even notice codec problems and we shot primarily in gardens and woodlands.
@Svart would love to see a trailer or something when you/they finish it. People don't believe me when I explain my reason for buying this over a 5d or 7d...I even lost a gig cause the guy(moron) didn't believe me about 24mbit ACVHD....its a well implemented codec and if you just change the log/trans setting to pro res (HQ)[*its (LT) by default] in FCP your footage looks awesome...seriously for 1k this is the BEST value in the video-world...period. And with the Hack it will just get better, and better...