I have a limited experience in editing HD video. The one thing I will say for the YouTube crowd, in my opinion, most people wont watch a video longer than a few minutes anyway. I, personally, have found that I like making shorter videos and uploading several of them. HD video editing gets more compounded when you throw in interlaced vs progressive and the many frame rates. There are a lot of little mistakes one can make to loose quality and not realize it until the several hour rendering process has finished. Saying that, I think your video looks great, and I also enjoyed your premise of a single spot with several different scenarios.
I use PC rather than Mac, though I don't believe any one is really better than the other. Its the same argument of vanilla vs chocolate, or ford vs chevy; stick with what you know or like, and only change if you want to learn more (or fancy a new challenge). When I started editing HD video several years ago, I was having similar problems with my computer crashing during uploads, my program (vegas Pro) locking up while editing, rendering freezing in the middle of production, and more. I built an entirely new computer with pretty much the best hardware I could throw at it. Amazing difference to say the least, and still running strong after probably more than 100 hours of HD video thrown at it.
If you are having problems capturing videos (I am assuming you mean adding them to your playlist in Final Cut Pro), I would first look at the actual hardware in your computer. What kind of processor are you using, how much ram, and what details can you provide of the hard drive? All three of these, compiled with the rest of your computer components, can greatly effect the speed and power of your computer. Your computer is only as strong as its weakest link.
Casey