The answer will vary depending on who you talk to. Don't call up reservations and ask - they could note your record making sure you don't even try and standby. I have not tried it with NW, but for the limited times I have used Priceline, I have been able to standby (and change flights) many times.

One last thing - use the kiosks to check-in! See if you can get any WP mileage (or OP) out of it. It never hurts to try - I am 12/12 on getting US segments to post to my Dividend Miles account.