Full body scanners - one more well thought out plan?

After the underpants bomber, the Transportation Security Administration is rushing to install 300 of  the full-body scanners everyone’s been talking about. The device appears work with some limitations but is very expensive so limiting the instillation to the busiest 300 of the nations 800 airports appears common sense. There is one possible flaw in this plan; if you were a terrorist would you expend any time or effort to get past the devices or would you simply get on a plane at one the 500 airports that don't have the equipment? Call me crazy but what's the return on investment here?