I've installed Mint 5 R1 Full, and all the multimedia is working beautifully except streaming windows media. MPlayer shows up in Firefox, says it's connecting, then says "Stopped". It's playing RealPlayer and Quicktime files fine. I tried reinstalling the win32 codecs, but that didn't help. Going through the media instructions for Ubuntu would seem like using a sledgehammer to crack a nut, since all other media are working perfectly, and it would be foolish to mess with it!
I did have a problem with Flash too, after installing updates, but I reinstalled that and it's working fine now.