If you're not already aware, YouTube doesn't exactly have "great" quality video. If you're uploading text, or a movie from the desktop it can be even more obvious that quality isn't high on the list of YouTubes priorities.
So, what to do?
- Capture at 1280x720 instead of the default YouTube size. We'll likely up the preset size in iShowU soon, or add an HD version specifically for YouTube.
- Don't have high degrees of scaling. That is: Don't record full screen to 640x480. The scaling itself reduces quality. Putting the scaled result through YouTube doesn't help matters. Try to record at close to 1:1. So if you're capturing 1280x720 make youre capture area that size as well for best result. 1280x720 should be OK if you're recording a laptop screen (full screen 1440x900) but "ok" can be subjective.
- Use an alternative service. Blip.TV provide higher quality and also lets the viewer see the original (uncompressed) video source.
You may also want to read: Recommeded Settings