YouTube announced in November that they would be testing out encoding videos at higher resolutions (and with higher-quality audio encoding). Now it appears that a small sampling of uploaded videos can already be seen at their higher resolutions, simply by adding a little tag to the end of the video's URL. To get a (slightly noticeable) bump in resolution, try adding
&fmt=6 to the end of the address line. The trick, according to YouTube watchers, seems to work primarily with newer videos, and bumps the resolution from 320x240 to 448x336. Add
&fmt=18 to the end of the URL, and you might get an MP4-encoded version, with better audio and a 480x360 resolution.