Cave In's website posted an update a few days ago about the former guitarist for Failure performing with the band on-stage during the Lollapalooza tour:

"Troy Van Leeuwen graced us with his prescence on-stage at the Lollapalooza show in Colombus, OH to assist in performing the Failure song "Magnified". Troy played guitar in Failure - the band we've not-so-secretly ripped off for years and years. He now plays guitar in Queens Of The Stone Age - the band many others will soon be not-so-secretly ripping off. Will more Troy/Cave In combinations take place on the tour? Stranger things have happened."