When I was deciding what to put on the Christmas wish list, it was either the Nikon D50 or the Pentax K100D.
I ended up going for the Nikon because it was supposed the be a more robust performer in terms of speed, and I'm glad I did.
If you, however, don't need more speed than the Fuji gives you now, then the K100D could be a better deal for you, as there aren't that many third party lenses to go with the D40(x) as there are for the K100D.
Assuming you don't want to shell out much on lenses to get you started, having good options with Tamron and Sigma can't be too bad, as they make decent lenses for the price and they often make for a good value.
The in-body shake reduction could be useful as well, although it might not be too useful all the time.
Then again, the D40(x) is rather speedy (burst mode, focusing in low light is supposed to be decent too like with the D50, which isn't too bad, even though it does hunt sometimes) and the kit lens that go with it aren't too bad either (neither are the Pentax kit lens, though).
One more thing to consider is whether you plan to shoot more in raw than in jpegs or vice versa.
