Lambda the Ultimate

I'm working on a simple, dynamically-typed language for business users. We're trying to have as few datatypes as possible to reduce the number of things they have to learn (currently just strings, numbers and tables). I'm considering just using "true" and "false" strings instead of boolean values. I can't see any arguments against it but I can't help feeling that I'm going to regret it.

Is this sensible? The only language I'm aware off that does something similar is TCL, which also allows yes/no/on/off.

EDIT: I suppose erlangs true/false atoms are similar. That gives me some encouragement.