I think this is BS anyways. Maybe because I'm asian or non-white, but I've never been allowed over the border in Buffalo/The Falls without a passport. Most recently, 4 years ago I got rejected with just my drivers licence, but got through cause I had an old TN visa kicking around in my wallet (which I had out of my passport to photocopy to fax it). The INS agent told me that I always need a passport or citzenship card, and the TN visa proved that someone had verified my citizenship within the last year.