But I've finally made up my mind, and gone for a Sony Nex3 with an 18-55mm lens, on the grounds that it has a big DSLR sensor and a teeny weeny body, so should offer good quality but still be small enough that I'm actually likely to take it out and about with me, (and it's also cheaper than any of the other options!)
I hope it turns out to be a good decision! On the plus side, if I'd been more decisive, I'd have bought a camera ages ago before this one came out, so YAY for indecisiveness.
I did wonder whether to get the Nex 5, which is basically the same camera but with HD video, IR connectivity, and a metal rather than plastic case for a hundred quid more. But I don't think I need HD video, and although I liked the last camera I owned with a metal case - it felt more solid and stylish than my current plastic one - I found that it was rather heavy and easy to drop. My current camera is plastic, and it's undeniably just that bit less likely to slip through your fingers, and easier to handle on cold days. And a hundred quid is not to be sniffed at!
I'm thinking that if all goes well, I may still eventually buy another compact ultrazoom as well rather than stick a monstrous zoom lense onto this tiny camera, so as to have the zoom available if I want it. I think I will miss the big zoom, so am planning to keep the Panasonic FZ7 as well for the time being.