Nothing is as bad as tech trading. No matter how far behind you or anyone else got in tech in Civ 4, all they had to do was get to one tech before everyone else and they'd instantly catch up through mass trading.
All this is said many times already, but tech trading could only got you on a par (at best) while Research Agreement throws you miles ahead of everyone else. If tech trading really was as exploitable as some claim, there would have been much more regular Deity-beaters.