My IR didn't arrive after two months, then three months. I called the Fort Worth FSDO, and they transferred me to a number where I left a message. Nothing happened. So I called again a week later and pushed harder for a response, and finally got told to phone a number in Oklahoma. I finally got hold of someone there, who informed me that there was a mistake on my application from the DPE (!!!!) and that they had informed him and were waiting for him to fix the application. The mistake was that he said the check ride was 14 hours instead of 1.4 hours. They said they would resubmit the request to the FSDO which would then contact the DPE... I offered to contact the DPE directly because I could see this was not going to happen quickly. Anyway, I managed to get hold of the DPE who was completely surprised and said he knew nothing about this. He contacted them and straightened it out, and I got my plastic card two week later.
Moral of the story is, stay on top of it, and if it takes longer than three months make sure you follow up and make sure there is not some silly paperwork issue.