LttP: PSPTube proves YouTube videos are possible
The download is available from Japanese homebrew developer, SofiyaCat. The latest download can always be found here. Obviously, a homebrew-capable PSP is required to run the program. After downloading the zip, move the appropriate folder to your PSP. (For example, 3.52 M33 owners will want to copy the PSPTube folder from 200over into PSP/GAME352, with the firmware set to 3.xx kernel.)
Then, you'll have to edit the psptube.cfg file with Notepad. You'll find a lot of weird looking text and then a line that says dev_id="". You'll have to acquire a YouTube developer account and throw in an account ID there. After that, you can launch the program from your PSP. Unfortunately, we were surprised to see that the program is not compatible with encrypted wi-fi signals, so make sure you go to an open network for best compatibility. The videos will play after a small amount of buffering, and will stretch to fill the entire PSP screen. It's not the best interface for YouTube, but we're still impressed by the results. Hopefully, Sony will see that YouTube support is very possible for PSP, and will include it in a future firmware update.
[Thanks to everyone that sent this in!]