I came back from an 11 day camping safari in Botswana last month and I brought a 7D, 5D2 and 1DIV, as well as a GH-2.
For the long lens work I used a Sigma 50-500 OS EF mount and Canon 70-200 IS II. The GH-2 had the 14-140 and 100-300.
I barely used the the GH-2 because it tended to be infuriating how the operating system and menus would 'lock' you out of modes that it didn't think you could or should be on. This annoying tendency made it really hard to like the camera since I'd wind up shooting jpeg when I wanted RAW, or be in crop mode (teleconvertor mode) when I wanted 'full frame'.
Also, while the AF was quick, the blackout period during fast shooting meant that I'd rarely be able to get the shot like I could on the 7D or 1DIV. Then again, the Panasonic was 1/3 to 1/5 the the price of the systems it was up against. Also the single mode rolly wheel wasn't very convenient when you have 3 wheels and a joystick on the Canons.
I'd also say the GH-2's construction felt flimsy, plastic and downright cheap, compared to my dad's GH-1.
I wound up using the GH-2 much less than I thought I would (probably 1% of my shooting), but I've been trying to give it more opportunities, since I hope that I will 'grok' the way it works once I have enough shots under my belt. Whoever wrote the manual should be shot and hung, then revived so they could be drawn and quartered. I've only seen worse manuals from industrial equipment manuals from low quantity production specialized foreign machine shops.
Optically, the 100-300 lens isn't bad...as a lightweight combo it was a no brainer for me to carry a full GH-2 setup along since the whole combination weighed less than one of the heavy lenses.
