Regarding the next YouTube Debate, only two GOP candidates have agreed to do it: Ron Paul and John McCain. This isn't shocking to me. Paul and McCain will do fine in a debate with unscripted and tough questions, because neither gives politically correct answers - they give honest ones. Speaking truthfully and frankly requires no preparation, just conviction. McCain, for example, has been on the Daily Show many times; he has parried the best that Jon Stewart can throw at him.
McCain and Paul are the only two republican candidates I'd consider voting for, though it is likely that I'll have no such chance for either. The rest of the GOP candidates are garbage. I'm not even sure why Romney was ever considered a "front runner", and it has been especially entertaining as of late to watch everyone come to realize how overrated Guliani is. It doesn't surprise me that they don't want to be asked the difficult questions - they don't have good answers. Still, I predict that the risk of looking completely disconnected from the mainstream will force them to show up to the debate, even if they are loath to.
A last comment. I think, perhaps wishfully, that McCain is going to make a turnaround. He really is the only solid player that the GOP has at this point (enter Thompson?). If McCain changes his Iraq policy to something more reasonable to the general public, I think he will have a 'surge' of support. And why wouldn't he (change his Iraq policy)? The situation in that country a year from now is going to be vastly different than it is now.