They are rated to 2.3V I believe. Crucial don't seem bothered as I actually RMA'd a set I'd put 2.5V through (by accident) and I told them as I actually wanted to know what the warranty position was and the guy said he didn't think it woul dbe the voltage anyway, and to send them back as the tech people would want to see them. Can you see why I bang on about Crucial's RMA service all the time now?
If they are VERY hot (can't touch them) then some active cooling may be in order to lengthen their life, but as most of us rotate kit inside a 12-18 month period, it probably isn't a problem for us, but rather for the folks we sell them to. Caveat emptor.