[mhcasey]

Not an expert here, but I believe weight and balance certification is based on a number of factors other than "can it still fly?" Example: Can we add another 200lbs, make a rough landing, and expect the gear to still be attached to the airplane?

I'm not sure this actually applies to any light singles, but there is also the issue of zero fuel weight.

By the way for any mislead noobs on this post...At some point adding enough weight will prevent the airplane from flying. Above posters are pointing out that a typical C172 a 100lbs over weight will still fly. Assumptions:

1) You're at a reasonably low density altitude.
2) You have no desire to reach a reasonably high density altitude.
3) You have no desire to reach a slightly higher but still low density altitude any time soon (poor climb rate).
4) You have enough runway to compensate for the increased ground roll on takeoff.
5) This list could go on for a long time...

When the power required curve is higher than the power available, you might get the plane into ground effect if you roll downhill, but you might not ever clear those trees at the end of the runway...