I've had the same experiecne YankeePride had with e-mail trades, but there have been times when I've gone back and offered the same trade and had it accepted, too. And after the seven-day window of opportunity was closed, too. (I had not stopped the game because I though the message would ony be a "we won Mothers' Day' message.)
But I have repeated my attempts to get solid players on the trading block with overwhelming offers and gotten nothing--even when I offer my all-star starter at the three positions the offering team needs.
I like Steve's answer because I've worked for a lot of people who acted that way.