Hmm. I'd agree that Nikon has the closest feel to Pentax, in that their cameras tend to have good handling and their higher-end bodies have lens backwards compatibility like we do (both of these points so
unlike Canon).
That said, every other company has something attractive to me. Olympus makes some really nice glass, and the compactness of the Micro 4/3 bodies is nice. Also, somehow most Olympus cameras produce really nice color. I used to be an Olympus user (Oly E-520), only switched to Pentax because I decided I wanted them Pentax primes. And the K-5 attracted me too. (Note: the Oly E-520 has dismal dynamic range and high ISOs, which sort of explains why I liked the K-5 so much)
Canon... well I really dislike the handling of Canon cameras, with the possible exception of the X0D series. But I think I like the color of Canon JPEGs (although I shoot mostly raw), and I sometimes like the 'look' produced by Canon glass better than them Nikkors (totally a subjective preference, nothing much to do with IQ).
The new Fujis are very, very tempting to me, especially the X-Pro 1. Very tempting with those primes. However, if I get them (will take a long time to pony up that amount of cash, heh), I wouldn't be jumping ship, rather I'd use the Fujis as a complementary system to my Pentaxes.
Leica, I actually don't like the M9, but the S2 attracts me. Then again our 645D attracts me even more. And in any case I'll have to wait till my next life, if I get reborn as a rich man, before I can even dream about getting one of those.