@Froberg & @DaLuke
Sorry for the delay in replying I wasn't following the post
For some reason plex is not updating for me,
Quite annoying, the code I posted before adds the plex repo the the ubunto repo.
Thus the Ninjas code "sudo apt-get update && sudo apt-get upgrade" should work.
It clears up the public key issue.
I know because I used it as an apt-install plex (and it worked)
deb http://plex.r.worldssl.net/ PlexMediaServer/ubuntu-repo lucid main (remove space after net/)
However it is still not "auto" updating -
The original link I found was http://wiki.plexapp.com/index.php/Downloads#Ubuntu_.2832-bit.29_-_PMS
My own PLEX is listed as 0.9.7.22 although the latest is 7.28 meaning mine is not auto updating either.
Maybe a Ninja might have a quick look at this.
UPDATE- after taking the time to read the forums and auto update feature seems to be broken for now,
see - http://forums.plexapp.com/index.php/topic/78362-ubuntu-repo-still-at-09722/
The link for the wiki.plexapp should help.
If not, let me know and ill keep looking.