There was an amusing short book a few years ago about how to write ambiguous lawsuit-proof recommendations for people in whom one had little confidence. One of my favorites lines this one:
"You will be very fortunate if you can get him to work for you."
This one, via Wizbang, might not be law-proof:
"Works well when under constant supervision and cornered like a rat in a trap."
Off topic, but I heard an amusing ambiguity on the radio news this week: "This holiday season, people spent more money than they had since 2006."