It's interesting that both of the comments so far seem to be discounting the idea based on frankly obvious arguments. That is, people think of a counterargument, and stop there. To me, the counter-counter-arguments are about equally obvious; and even if they were not, it would be wise to consider the possibility they exist.
I'm not arguing that I'm necessarily correct here (insofar as that's even knowable currently), but just that, from my perspective, it seems that people are dismissing my idea too lightly. The possibility of simulation is so much a part of Less Wrong culture that there is a vocabulary of over a half dozen terms to describe related sub-ideas. If its very foundations are questionable, I would say that that deserves proper discussion. And "your first draft was too short", insofar as it's contributing to my down-rating, seems an especially poor reasoning.
Edit: as the discussion has progressed, I no longer find this to be a currently valid observation, yet I still think it was valid when I first made it.
Well, your reasoning appears to be, "A simulation of our universe would require vastly immense computational resources. Things that require vastly immense computational resources are vanishingly unlikely. Therefore, the existence of a simulation of our universe is vanishingly unlikely." I can't think of an argument for the second premise.
ETA: well, I can think of one argument: "A universe with vastly immense computational resources would have a very high Kolmogorov complexity." This is false, however, as, for example, Conway's Game of L...
I've written a prior post about how I think that the Everett branching factor of reality dominates that of any plausible simulation, whether the latter is run on a Von Neumann machine, on a quantum machine, or on some hybrid; and thus the probability and utility weight that should be assigned to simulations in general is negligible. I also argued that the fact that we live in an apparently quantum-branching world could be construed as weak anthropic evidence for this idea. My prior post was down-modded into oblivion for reasons that are not relevant here (style, etc.) If I were to replace this text you're reading with a version of that idea which was more fully-argued, but still stylistically-neutral (unlike my prior post), would people be interested?