I agree with Brian that their "big" camera is a more likely candidate for a refresh, since it's farther along in the development cycle and the GF-1 seems to be selling briskly (it's not even available body-only yet, AFAIK.)
My question is whether they're going to continue to bother having non-video and video models within the "big-camera" subline. I think it would be more logical for them to pare down their Micro Four Thirds lineup to one compact model with "consumer" video features (GF-x) and one larger model with "prosumer" video features (GH-x.)
Under this logic the GH-x model would get refreshed next with the new sensor and whatever other goodies they've got in the back room (e.g. eye-level finder with their new high-res LCD, as on the EP-2's accessory finder, instead of the expensive sequential display) and then the GF-x model would get a corresponding refresh a few months later, and then they'd continue to alternate updates between the two product lines.
I also wonder whether they'd continue calling it GH-2, GH-3, etc., or adopt Nikon's convention of calling it, say, "GH-1s"...
I also endorse what has been said and add my two pennyworth.
The GF1 was only released latter part of last year so I would not expect to see an updated version until the end of 2010 at the earliest, it is selling very well in the UK and only now are we finding supplies of body only & 20mm lens on its own being available - the continent is still struggling to get the kit with 20mm.
I suspect as do others that Panasonic will merge the G1/GH1 into a new camera and that will appear later in the year. I do not see them announcing a GF1 replacement until well after a G1/GH1 so as not to impact on those sales.
I also suspect Panasonic will wait and watch to see what Olympus do next before showing their hand.