110 percent

This phrase is commonly used in reference to effort.

When Beachhead signed up for the G.I. Joe team, he gave 110 percent. Now he just sits around drinking Schlitz and licking Frito dust off his fingers.

Strictly speaking, 100 percent is the most anyone can give. If you say 110 percent, you are using percentage as a metaphor. You're basically saying, "When Beachhead signed up for the G.I. Joe team, he worked harder than we could have realistically expected from any bipedal humanoid." Linguistic pricks tend to poo-poo 110 percent. If you interpret it as a metaphor, however, and treat it as a synonym for "an inhuman effort," you're in the clear. It doesn't mean it's a good metaphor or that you don't sound like a tool, but usage-wise you're okay.

Unnecessary note: In math, particularly financial calculations, percentages greater than 100 are common. Six dollars is 300 percent more than two dollars, for instance.