I've blogged before on my pet peeves with some of the common mistakes in professional writing.
Today, Jonathan Chait in The New Republic quotes a Clinton memo: "Democrats may have a nominee who will be a lightening rod of controversy."
Enough with the enlightenment! Here's another memo: "lightening" is reducing the weight of something. "Lightning", on the other hand, is a spontaneous discharge of built up static electricity in the atmosphere. The rod is meant to attract lightning, not reduce weight.
While we're at it, you "toe" the line, not "tow" it.