There's a substantial difference between the GH1 and E-PL1 video performance.
The GH1, with all its functions, full HD, 50p etc. is pretty close to being a broadcast quality video camera in its own right. I've seen stuff shot with the hacked firmware that is just breathtaking. The E-PL1 isn't in the same class really, though in its own right is very acceptable. It has excellent colour for example and isn't too bad for recording motion.
Lenses don't seem to make anywhere near the same difference to video as they do for stills and there's very little difference between the two zooms.
The Panasonic lens has the advantage of its silent smooth AF but the E-PL1 output isn't sharp or detailed enough to reveal any difference between the lenses.
I'm a little bit disappointed with the Olympus video, considering that its the same sensor as the Panasonic. Its very much the same with the Samsung NX10. It produces tremendous stills but the video is terrible, riddled with CA and moire. The Olympus output is better than that, but is still too soft for my liking. The output from the GH1 is virtually indistinguishable from cameras such as the Canon 5D Mk II & 7D, and viewed via an HD TV is just spectacular.
With all the rumours circulating about an Olympus 'modular' camera, which I presume is going to have video, I think Olympus need to look at making substantial improvements to their video output if they are going to come up with something that is truly usable. This obviously seems to have to do with companies experience of producing video cameras. Nikon are in the same boat. The D3S is I gather better, but is still behind the standard of what Canon can produce.
With my partner I'm currently in the process of making a documentary using both Canons and two GH1's. We've shot weddings, events, scientific and commercial videos using GH1's, and have even used a GF1, but we wouldn't even consider using any of the Olympus cameras for that. We get a better result from a £300 Canon domestic camcorder, with a very small sensor, than we do from the Olympus's.
Having said all that, if what is wanted is video for holiday & domestic use then the E-PL1 is certainly up to that. Its just that using a GH1 makes us expect a lot more. Having seen what the sensor is capable of on that camera, it seems strange that the Olympus output shouldn't be comparable.