Rag2177,
It sounds as if our sons have very similar habits. I don't know if you read about my son (he's 9)in earlier posts, but he too, recently told me that he counts letters not only while people are talking but on the wall, within the books he's reading, signage, etc. He also has some other number issues as well. He is also a very bright child and is constantly moving and talking. He's always been that way. He talks nonstop (even in his sleep). Does your son have any tics or involuntary twitching? My son does, but it's very mild.
I took my son to the doctor and he suggested not to worry about it unless I see that it's interfering with his everyday life. I, too, can see his little mind racing while we're talking to him...now I know that he's counting our words. I don't see that it's affecting him in a negative way; however, he has asked me to find a way to help him stop. I still haven't figured out how without medication (which we're opposed to for now).
By the way, the doctor doesn't consider this TRUE OCD unless it interferes with his daily routine. Have you taken your son to the doctor?
I'm looking forward to hearing from you.
sbechtel