(Note that all Micro Four-Thirds lens focal lengths given below need to be doubled to get a 35mm equivalent.)
Unlike autopope, I decided to go for a Micro Four-Thirds camera, the Panasonic GF1, with the 20mm f/1.7 prime lens included, and also the 45-200mm zoom. With £50 cashback from Panasonic, I won't lose any money if I decide to keep the lenses and sell the body on eBay, and buy an Olympus body instead.
The plan is to have a camera (with the 20mm lens) that I can easily carry around on holidays and excursions (It's just about pocketable, with largish pockets), with the zoom in the camera bag for times when I think I'll need it.
(The following is according to reviews, not personal experience.) The GF1's advantages over the Olympus E-P2 are quicker auto-focus, a better prime lens bundled with the camera, and it's cheaper. The Olympus's advantages are better JPEG processing, wider range of art filters built in, in-body image stabilisation (so it stabilises all lenses, and not just those with Panasonic's in-lens stabilisation built in), and a high quality electronic viewfinder (the Panasonic has a much worse one as an optional extra, which I've not bought). The first two of these can (I hope) largely be overcome by shooting raw and processing in Aperture.
I also quite fancy a wide angle lens (Panasonic do an extremely good one that's mind-bogglingly expensive) and a macro lens (Leica do a nice-looking 45mm f/2.8 one), which is also pretty expensive. And Panasonic are coming out with a 100-300mm superzoom later in the year. But this way lies madness, or at least bankruptcy. Of course, if I don't mind manual focussing, there's a large array of lens adaptors available, and thus access to lots of other lenses (although probably not anything with a very wide angle, due to the doubling of the effective focal length from the smaller sensor).