I own and really enjoy using the LX3 but I am very interested in the G1 as a lightweight two camera travel combination. I managed to have a look at both the G1 and E-P1 last week but liked the swivel screen of the G1 and the option of the EVF. I have various A3 prints from the LX3 framed on the walls so I am sure the G1 would have no problem with this size. Does anybody shoot with both of these cameras together when they go on holidays?
Yes, if you substitute the D-Lux 4 for the LX3, that´s my present arsenal (together with my cherished Digilux 2 for special occasions...).
I can tell you they complement each other quite well (if you really need to complement the LX3, that is. More about that later). The G1 provides a big sensor, a (perfectly usable) eye-level EVF, and a swivelling screen, also a decent range of lenses (plus a huge number of legacy ones): it´s almost the equal of a dSLR system with one fourth the bulk (if you have a few lenses). The DL4 (and assuredly the LX3 as well) is a great pocket camera, with small sensor, fixed short but fast zoom and "less comprehensive viewfinder solutions", to coin a silly phrase. But, it does contribute about half of my shots, and I seldom have to make any excuses for the IQ, even when the images are displayed beside the G1 ones.
Never handled an EP-1, but it seems one would trade-off all of the G1´s viewfinder advantages (going right "down" to the DL4 level) just to get a little bit smaller camera body. While the Olympus does look sexy, and the G1 looks more or less like a Fisher-Price version of an SLR, I don´t even contemplate swapping the G1 for the EP-1...
All that said, if you already own, use, and like the LX3, you should sit down and think just what you would get from the G1 that the LX3 doesn´t already provide:
Wider range of focal lengths? Sure, but you´ll have to carry extra lenses and change them all the time.
Less noise in low light? Yes, but not quite as much as one might think, since the lenses are much slower (the Pana zooms; shooting with legacy lenses is something of a hassle unless one shoots portraits, still life & c).
Faster AF and card writing? Yes, a little, but not much.
Higher IQ? Not really. Colours and contrast in my DL4 images beat the G1 ones noticeably direct from the camera (I shoot raw; in jpg the difference is even bigger). PP does help the G1 shots, but there´s still a difference.
My own order of acquisition was the opposite from yours: I had the G1 first, and bought the DL4 later, "just for when I absolutely couldn´t carry a bag". I´m surprised at how much the DL4 has taken over, even when I do have a bag. But you have to think and decide for yourself.