Lots of questions!
First of all, most consumers are making the move to High Definition Video Cameras. It's a great thing to have if you're looking to be having the camera for a while. The Youtube buffering thing is relative. If you have a higher speed internet connection, it should take next to nothing for HD Youtube videos to buffer. On the other hand, if you have a slow connection, it'll take a while for it to buffer before you can watch it. Keep in mind, though, if you upload an HD video to Youtube, when someone watches it, it will give them a choice to watch it in HD or Standard Definition, this gives people with a slower connection a chance to watch your video anyway. Most new HD cameras will record in standard def, if you really want them to. And yes, there are many different storage formats to store your videos on. Most older cameras had tapes, while the newer HD cameras have split into roughly two sections, ones with SD cards, and those with HDD drives. I use a Sanyo Xacti HD1010, and it's 1080P (full HD) quality, and I love it. It records onto an SD card, and the pro to having an SD card camera is that it's very portable. You can just pop it out and slide it in to your computer. The downside is that they don't make large size SD cards. I have an 8GB card and that'll record High Def for about 30 minutes.
Please rate, as it makes the world go round!