I have been working with the strengths and weaknesses of the 5n for several months now. You can do a lot with the camera considering its weaknesses - handling issues you can adjust too. The sensor is fabulous and I would take it over the any of the hacked gf models for sure - better ergonomics than the gf's, the sensor performance, very good codec, 1080 60p, incredible stills when you take them (dynamic range, high iso, etc.)
I like the video from it better than from the Nex-7. Yes, I have also seen that blochy video noise at 1600 and 3200 iso when I have pushed it. Sunset seemed a better than portrait profile in those instances. I've shot at 3200 in b/w with contrast and sharpness ramped down and it looked gorgeous. Also shooting primarily with FD glass.
Protect your highlights when shooting with the 5n - they blow-out fast. The type of shooting I, overheating has only twice been an issue. I generally shoot short clips of interviews, scenes, etc. But the few times I have had a shot cut short due to overheating, it was a major bummer and I wanted a gh2 right then and there.
All that said, the gh2 is a much more capable, all-round camera for video and I am definitely purchasing one now that I've worked with the 5n for these months. I'll still use the 5n, but the gh2 quality even with basic hacks is so impressive. There are folks hacking and making solid improvements to the audio:
http://www.personal-view.com/talks/discussion/1152/gh2-audio-hacks/p5
I've spent hundreds getting good audio for the 5n which I then have to sync later. Quality is great but it is extra steps and all the money adds up. I very much understand being on a tight budget. Depending what you want to do, you may spend the difference between the 5n and the gh2 on an external recorder alone... (ps. do not get a h4n. for the price, there is better equipment now.)
Even without the gh2, Andrew's book has been very helpful, fun, inspiring.