It has been widely reported that the drug test failure was due to marijuana use and not a PED positive. Either way, it was his second violation of baseball's drug policy and has landed him on the restricted list to begin the 2014 season. I am guessing that he is hanging around extended Spring Training. While there are clearly some issues surrounding the Rays former first round draft pick, there is also plenty of talent still waiting to be harnessed.
Guerrieri has pitched in parts of the 2012 and 2013 seasons posting an ERA of 1.04 in 52 innings in Low A during the 2012 season and a 2.01 ERA in 67 innings in High A last season. Add in the fact that he's also kept his WHIP below 1 at both stops and has 96 strike outs versus 16 walks and it seems that the Rays still have the makings of a good pitcher.
Guerrieri had a few nice rookie autographs floating around after he was selected in the first round of the 2011 draft, but his card values has tumbled with his drug suspension. Patient collectors can find them in the figurative Ebay dumpster around $0.99. If you get really lucky you can find a $0.99 listing with free shipping. Seriously, if Cardinals General Manager John Mozeliak were shopping for Taylor Guerrieri autographs he would label him "low hanging fruit". I recently pulled off a 2012 Bowman autograph for $0.99, but I piad $1.50 in shipping. Steeeep.
Still for $0.99 starting bid, and likely closing bid, you could search out some 1996 Leaf Signature cards of Gregg Colbrunn and Jon Nunnally, or you could go find a Taylor Guerrieri. Only one of those players has any upside left to their hobby value. It's a bit of a gamble, but if the Rays can help Guerrieri right the ship he should be a pretty good pitcher with ice card value.