I'll throw in my experience as well!
I purchased an SU-16 in August last year, and by late October I was suffering from a cracked receiver area much like the other pictures I've seen. I first e-mailed Kel-Tec, who then told me (quick response!) to send it back through whomever I purchased it from initially. Unfortunately for me, that place was Del Selins in Vernon...which should make most folks from the interior of BC cringe with pain.
It was 10 weeks and a bit of harassment in Del's direction before I got a call from Gary at Vault, saying he had my rifle in hand and was going to replace it. It has been another 5 or 6 since then waiting for it to be sent back to me. Though in Vault's defense, the wait time hasn't entirely been their fault, as they have had a hell of a time getting anything over the border these days. I was told my replacement SU-16 would be in the mail this coming monday, and I've got my fingers crossed it's for real this time!
Despite the (almost) four month elapsed time, I still plan on keeping and using my SU-16 when it is returned to me. It's just too much fun to shoot. Hell, I'm not even turned off of Kel-Tec; looking at a Sub-2000