> Also, make sure you tell them you are on TN status or they will happily wave you through on B1 which you won't know until you download your updated I94.

Bingo. I had the unfortunate experience of crossing after obtaining a renewal through USCIS, but before my original TN had expired.

Despite giving them all of documentation, including the I-797A and new I94, the agent entered me based on my old TN, which expired.... a couple days later.