When I lived in Texas in the early/mid 80's, I had both a Texas ID & DL. At the time, the state had no problem with me having both. I used the ID for checks & the DL for the police (I got pulled over only once for a taillight, had Michigan plates/insurance & Texas DL--policeman said since I was a student having MI plates/insur. was OK. The situation in the earlier thread reminds me of the merchants asking for Soc. Sec. #, not really necessary IMHO but was part of lots of store policy, etc.