Converting objects to type Bool
I'd criticize:


Extension methods on "object" should be avoided because of the broad scope, except for special cases (which such a "ToBool" method is not one). It also feels like an overuse of extension methods.
The first one takes an "object", but really wants a string, and will blow up with an InvalidCastException at runtime.
The second one does not check for null (which wouldn't be a problem in itself, but having overloads for default values with differing behavior is bad).