Can a Jedi lightsaber cut through Superman? Short Answer: No

I love Yahoo Answers, only because they have tons of stupid questions such as "Can a Jedi lightsaber cut through Superman?" and great answers from people who really know their stuff. From Yahoo Answers:

RED LIGHTSABERS
Superman receives his power from the radiation of our yellow sun, and is weakened when exposed to radiation from a red sun. It is possible that a sith lightsaber, being red, might have similar properties.

Even so, Superboy Prime was defeated after being plunged through Krypton's red sun - which weakened him, but did not destroy him. Therefore, a red lightsaber which hypothetically had the same properties as a red star should have a similar effect, i.e. it would injure him, but not "cut" him, much less cut through him.

FORCE OF IMPACT
If Superman were rendered vulnerable by a lightsaber, it would likely create a momentary weakness in that spot, allowing the physical impact to cause damage. However, lightsaber blades, being made of plasma, presumably have a very small mass. Therefore, the force of the impact would be negligible.

In short, hitting Superman with a red lightsaber is like hitting a normal human with a wet noodle.