This thread reminds me why I <3 this board so much! Nothing like a good nerd/geek/dork debate (between a bunch of nerds, geeks and dorks, of course :)
Science puns have an appropriate time and place (although I'll readily admit that I'm guilty of spouting them randomly in the lab at work...typically at somewhat inoppertune moments [during meetings, etc]). (I can't say if the following apply to geeks and dorks, but I think they might)
*In the company of non-nerds, or nerds who have yet to accept their nerdiness (I'm looking at you Betty :), science puns are even less cool than normal.
*In the company of fellow nerds, science puns are slightly more acceptable but still not always appropriate (serious meetings with the boss are one of these moments, but at less serious meetings, the boss often finds the joke funnier than the coworkers). Some coworkers (usually the dorks) will never find puns or jokes of any kind humorous, so the hilarity of a given pun should never be judged by their reactions.
*Finally, in the company of drunken fellow nerds, science puns are often at their most hilarious. This can either be attributed to the interactions of good old ethanol with the pun-listener's humor system (a very scientific entity :) or due to a certain loosening of the pun-teller's sense of propriety and nerdiness. AKA a certain amount of EtOH always makes you funnier (I've done my fair share of testing this theory and so far it holds true). There's also the competing theory that activities involving EtOH (happy hour, lab parties, etc) also select for a specific cohort of nerds, that is, those who are capable of loosening up a bit (with or without the EtOH), and those who are uptight and dull are under-represented in the sample so results of humor-tests (such as puns) are biased towards being funny in this environment.