There was a hot minute in 2010 where Sleep was covering Ozzy Osbourne's 1981 track "Over The Mountain" as a gloriously stonery jam and it was fantastic. According to Setlist.fm, the cover got performed seven times throughout 2010 and once in 2011, and then was retired forever (so far).
Check out Sleep's rendition of the classic metal track above, filmed in Denver, CO on September 5, 2010. Again, we really need Sleep to do a studio version of this one.
As far as any activity in the Sleep camp, it's been pretty minimal. Sleep reissued Dopesmoker last August with a previously unreleased track "Hot Lava Man," and played a handful of shows around the annual April 20 holiday for stoners. Other than that, it seems like Matt Pike is spending his time these days working on a new High On Fire record.