I've also been using mosly Forte (or whatever Performance branded them as before) tubes since at least 2004. I think that I've had, at most, 2 valve failures and those have always happened after the tube had been in use for several months. So you either got a bad batch, or as Psimet said you've got something embedded in your tire, or the rim tape is not fully covering the valve hole (if the rim valve hole has some roughness, this might rub against the base of the tube valve and mess it up). Again, I've had nothing but good luck with Forte tubes and many other Performance house brand stuff (I've got a red Ascent branded floor pump that just refuses to die...I've had to return Topeak and Park pumps in the past but my cheapo red Performance pump still works like a charm!)