I regularly leave my car undriven for weeks at a time, and it always runs fine. If your car is to be left for any period again, I recommend disconnecting the battery.
If you want to be on the safe side, an oil change wouldn't hurt either.
Jack Travis, E-Series Acting President
1989 Ford Fairmont Ghia turbo/GL replica (underway)
1994 Eunos 800M
1990 Ford Laser S