Extensive LED info at...

[RonM]

SuperBrightLEDs.com has some really detailed data sheets with neat graphs for their LEDs. For an example click here.

I found the Relative Intensity vs. Ambient Temp graph to be very interesting. Didn't realize LEDs got that much brighter by being run at colder temps.

 

[Entropy]

Yup. Cold temps do two things:

Allow the LED to run more efficiently (reducing heat generated)

Allow the LED to run at higher powers (by removing heat more quickly)

Heavy cooling of an LED is the exact opposite of thermal runaway (where the LED becomes less and less efficient and heats up more and more until it blows.)

With extreme cooling (LN2), a 1W Luxeon should be able to hit 10W easily.