Just to add my grain of salt to the anti-canard topic (sorry about thread hijacking).
Did you notice that an ovewhelming majority of gliders still use the classical wing-tailplane combination. There have been some rather unsuccessfull canards (Dick Rutan's Solitaire is probably not his best achievement) or flying wings, but basically none achieved better performance with equivalent handling.
This has to do with one of the facts pointed out by
volume:
You can state in general, that for static stability reasons wing loading of the canard must alwys be higher as the wing loading of the main wing. This means your canard always operates at higher Cl than the main wing.
This is especially bad for gliders who spend a significant time flying at low speeds, hence close to max Cl for the wing.
Note : before someone starts flaming me, I know that gliders are not airliners, but there are some commonalities there (efficiency requires high L/D, hence high aspect ratio and similar "tricks" to operate close to max L/D in cruise, altitude for airliners, ballast for gliders)