I knew I should have went to Rome! At this past weekend's "Jus in Bello" convention in Italy, Jensen Ackles and his pal Jason Manns treated the crowd to an "impromptu" rendition of "The Weight." Jensen strums guitar expertly, despite claiming to not have rehearsed. This solidifies it: next year, I will drag (and throw on a stage) a guitar to Creation Entertainment's LACon so he can't claim he can't sing just because he doesn't have any music!
There is a very long "vamping" intro on this. The actual singing is only about 3 minutes long. Feel free to skip forward in the clip for the good stuff!