This is where Southwest Shines!
This is what I like about WN - you show up at the airport a little too close to departure time, they will still check you in (at a certain cutoff the kiosk can't but an agent still can) and they will still try to get your bags through - making it clear if you're cutting it close - its not their fault if the bags are late. You can move towards the checkpoint and hope for the best - and honestly, in alot of airports at non peak times of day - you can get through security in 5 minutes.
Contrast this with USAir and others, read the stories on other forms "I was in line, tried to check in at 29 minutes before my flight, the kiosk wouldn't let me, the agent chastized me for being late and was rude (or even on Delta from an account on a-net - they imposed the same day change on the customer, no "flat tire" rule, for the next flight.) I tried to plead that I could still make the flight because it was 9:00PM in a non busy airport, etc.......
Way to Go WN!