If you don't check in 2 hours early for an international flight the airline can and (if necessary) will give away your seat. I've seen it happen and no amount of wailing or pleading changed the situation.

I'm not sure what airlines you are using, but the last two times I have left International on US Air, I've been in LINE at check-in for 1-1.5 hours. (It might not be so bad right now, as it's pretty slow in Belize right now). Then, you still have to go thru security, grab a drink at Jets, hit the duty free, grab a drink at Jets, buy your last second souvenirs, and yep, you guessed it, grab a last drink at Jets..... and they start boarding really early for those International flights.