I am glad you have already done your homework and have shortlisted some of the cameras. Generally 4/3 and m4/3 cameras like GF1 and Olympus EP-1/2 are good but supposedly a little short on the high ISO (I assume that's what you mean since GH1 is still around the size of D3000 whereas GF1/EP-1 is more comparable with LX3). It's still a lot better than PnS though, and really, unless you're comparing against the higher ended stuffs like Nikon's D3X, the differences are subtle (but noticeable) - you won't be doing high-speed, low-light shooting, although with RAW files, you can choose one or the other. Panasonic's G series are faster in focusing (their CF detect autofocus is comparable with entry level DSLRs) but a little short on colours while Olympus's EP-1 are supposed to be better in colour rendition (but a little short on autofocus abilities). Either way, with a zoom lens, they will be bigger than PnS - only if you wanna do away with zoom and just use the pancakes (and Pana has a very good 20mm f1.7 pancake).
There are other considerations like how you won't need a dry box for your PnS but will most likely need one for anything with interchangeable lens.
This advise is coming to you from a very happy G1 user (more than a year) who never regretted getting his G1 but is now using a D5000 (mostly because of lack of lens support compared to Canikon but it's been growing).