HD videos uploaded in 1920 x 1080/p will – probably – be transcoded by Youtube into 1080p videos. This represents an upgrade from Youtube’s 1280 x 720p maximum HD resolution. (“Probably” because Youtube says not all videos will be converted just yet.)
The 1080p videos, however, are useless for most computer displays as few have 1920 x 1080 sized displays. The main advantage, probably, is that in a near future world, we will be watching streaming videos over the Internet – on our real HDTVs, arriving via a set top box.
Worse, you’ll need a very fast processor to watch the new 1080/p HD videos. I can’t watch them on a 3.2 Ghz Windows OS computer – and I can watch them on my quad core Mac Pro only if I wait for the video to download entirely, first. The problem is the video stutters badly as the processor cannot keep up with the Flash video decoding.
Recommendation: Upload the HD video but don’t select the HD option during play back. It looks like the new “normal” is 1280 x 720 – so you don’t need to select HD.