I needed to calculate a free energy today. I knew the equation I needed to use. And it involved Faraday's constant. I looked at a table of F values (with various units) and none of them seemed to make sense. I figured out how to get free energy in units of (mv*C*kcal)/mol, which seemed fairly unreasonable. So finally, after thinking through several possible values/units of F, I gave up and e-mailed my PI. Turns out the solution to my problems is knowing that volt=joule/coulomb. Somehow I don't think I EVER knew this.
So of course, I head to Wikipedia, where I find out that not only can joules be defined as kg*m2/s2 i.e. Newton meters, they can also be defined as the work required to move a charge of one coulomb through one volt potential difference! Obviously my physics teachers failed to prepare me for real life, because I swear I've only ever heard the Newton meter definition.