If you're wondering why I'd want to target the air, it's because I mainly work off my Air and don't want the hassle of an external drive, thumb drive, file syncing, etc. So obviously there's a big performance loss for target disk mode.
We decided to go for the gusto in our first test and installed a 240GB OWC Mercury Extreme Pro 6G SSD into the Main bay of our 2011 Thunderbolt port equipped 13-inch MacBook Pro.