Check out this video:
Sunset, Superman, baseball.
It's one of Bryan Singers' video diaries. Nice to see them using practical effects!
I made my own lemon cannon with the help of my physics teacher uncle, Jonathan. Mine runs on combustion and not compressed air, however. We use engine starter in a can. It's pretty dang fun, and my house in Carlsbad is ideal for it. We have a big canyon behind our house that we can fire into with impunity.
Mike probably remembers firing it. I remember that was the day he brought over his limited edition Ghost Obi-Wan, which is about as nerdy a memory as you can have. Do we balance out the nerdiness with our use of internal combustion cannons? You decide.