Actually, answering that last question led to an interesting thought. Ease of computation puts an ordering on the universes that can simulate each other. If our prior probability of the universe existing is can be thought of as a function of ease of computation in the universe (probably not, but simplifying), that puts an upper limit on the "tower o' universes." Then we can make assumptions about how rarely universes bother to simulate whole other universes and actually get finite numbers rather than pesky infinities! Thinking this has caused me to revise my probability of being in a simulation down.
My father, who is home recovering from surgery, emailed the following web page to me and a few other members of my family, and expressed interest in reading interesting responses.
Any thoughts?