Has anyone got pregnant following their partner/husbands vasectomy?

I gave birth to our 4th child December 09 and we decided this was the best option for us as we decided we didnt want anymore. We've had the confirmation letter confirming my husband gave 2 negative samples and that its now safe to have without contraception. My monthly cycle regulated itself pretty much within a couple of months and its always 28 days dead on. I was due on my period yesterday and i'm starting to get slightly concerned thats its not yet made its appearence and doesn't seem to be showing any signs of making one either!! My question is has anyone got pregnant after hubby has had a vasectomy and having had 2 negative results?