I just realized that your question is not really about connectors, but rather the capability of netbooks for handling flash video.
I'm sure they have no problem with let's say standard resolution (360, 480) Youtube videos. The situation gets more interesting with HD resolutions (720, 1080). Recent video chips (either separate video cards or the ones built into processors) support HD video decoding by hardware, which means they can easily do it with low power consumption and low processor usage.
I suggest you look for this feature in the product descriptions, they usually emphasize it can handle HD video. Or if you have a nice model in mind, you can ask the forum about that.