The scan bar effect will vary a lot based on what you are filming. If you get the right monitor, with the right system, and the right camera, you can record a screen surprisingly well at times. For example,
For real captures, depends on what you want to do, capturing pure RGB is possible, and is the best way, but you need some really pricey equipment. For me, I generally just stick with a DVD-HDD recorder and S-Video. For youtube, it's good enough. And I find that good quality DVD recorders can usually be had cheaper then a decent capture card. The few cheapo USB capture devices I've tried have all been garbage.
As for a camera, a lot of people want the HD crap. But for youtube, who cares? I bought this beast for almost nothing, 480p, digital options, really nice lens. I'll take this over a mediocre HD camera any day. It uses MiniDV tapes, which aren't the cheapest medium, and require winding, but I've grown quite fond of it. I need to get a real digital reciever one of these days...