How often should I clean my bike? How often should I clean my bike?

I've used it several times over the summer, but only once in muddy conditions, should I clean it after every ride or once per quarter?
There's a saying that a clean bike is a happy bike. You really can't clean a bike too much.

Make sure to clean the bike more often in the winter when riding on road salt, which is bad for the drivetrain. 

For all bikes, I'd definitely clean the drivetrain if it gets muddy. Mud can interfere with shifting and braking. 

Do not put oil or grease on the rims. If you have rim brakes, they may squeak after cleaning the rims. As long as it doesn't interfere with braking power, I don't worry about that. The clean-rim-squeal-sound goes away on its own after a bit. 

In terms of the frame: With a steel frame, you'll need to worry about rust, particularly where you have any scratches in the paint. Patting the bike dry after a ride in the rain should deal with that. 

(This applies to steel and aluminum, I know very little about carbon or Titanium frames, or about disc brakes.)