Have you finished with Colt? I think this is still worth completing before we proceed to HPPC. Just talked to Staszek, we will move HPPC code to Carrot2 labs SVN repository (sourceforge) because we want to get rid of PCJ as soon as possible and need something versioned and sticky. I plan to make a few additions to HPPC that I could work on while you're completing the Colt stuff. Hopefully we can also get this ArrayIndexOutOfBounds beast in the mean time.
If you're done with Colt, I can commit directly to Mahout's branch and work from there. Dawid