When I'm performing quick calculations or estimates, measuring things, or balancing my checkbook, I just hit Command + Spacebar, then type in what I need to know.
- 1+1? (Spotlight gives the answer right away: 2)
- ((1+1)/4*(232.2-28))+55? (Spotlight gives the answer right away: 157.1
Instant math... way better than any calculator or calculator app I've ever used... and it's always at my fingertips.
Bonus: press Command + C to copy the result to the clipboard. Awesome.