the repo was well added, but I had the error that the 'opam' package was not found. I'm running Ubuntu Precise on a 64-bit machine. From what I see here:
https://launchpad.net/~avsm/+archive/ppa/+packages
it seems that the opam package is only available for Raring... But on the "testing" repository, I confirm that opam is available, even for Precise - though I didn't install it that way.