Same thing happened to me, also about three weeks past my purchase anniversary (April 30 2013) but on the driver side. Was about 10 inches long yesterday (and this morning), but then by the afternoon had cracked another 6 inches. Strange that there's no impact mark or spider-webbing - just one long, snaking hairline crack. I can't swear it wasn't initially caused by impact but I noticed it when I came out to my car after being inside. The new cracking definitely happened all on its own. I called my insurance for a quote on replacing the glass and it's just over $500 (unfortunately that's also my deductible...) but at this point I'm afraid that if I don't fix it the whole windshield might fail after a couple more thermal expansion cycles.