Short story here...
I mainly just shoot sports (small college). My wife thinks all you really need is one len. Anyway, I have the 40D, 50&85, 70-200 2.8, but NO FLASH
So wife ask me what I wanted for my b'day. I told her a flash for my camera.
She says "all you ever want is expensive camera stuff". I quickly tell her I do not have a flash and sends her an Amazon listing showing the Canon 580EXII.
She looks at it and tell me to order it if I really wanted it. (Note-she said wanted not needed)
So I got the flash today. You don't use a flash for baseball, softball, tennis, volleyball, or football, so why do I need a flash??
Cheerleaders, dance team, etc (But don't tell her)