I thought one flash was great, two is amazing! I setup my wife's 580EX with a Lumiquest LTP (thank you Lumiquest!) and my 550EX with the Lumiquest III. Set both flashes to manual mode and dial the power till I got what I wanted which took about 5 test shots. That's it! It's actually pretty simple to do. I need light stands. I was limited to placing the flashes on the table. But for now I'm very happy with the setup.
550EX with Lumiquest III on the left and 580EX with Lumiquest LTP on the right.