Ours puts out some ugly black smoke through the chimney, but it's never been in the house (knock on wood).
Every year I change the filter, the spray nozzle, clean the electrodes, and clean out the inside of the furnace (as best I can). There's a few guys in the area that do a "tune-up" for around $100, but I don't know what that entails. I just know that my limited handywork has so far worked out ok.
But the damn thing still scares the **** outta me. Especially when you prime it three or four times and it doesn't catch. Then, when it does..... WOOOOOOOSH!!! I've almost crapped my pants down there on more than one occasion.
Good luck!