Are franchise non-compete's enforceable?

Yes, a franchise non-compete is enforceable. As for reasonable terms: it varies with the situation and the industry/market. For, say, a restaurant franchise: a reasonable noncompete would probably be to not open any restaurant (franchise or not) which competes with the franchise (same market, same customers) in, say, a 10 mile  radius. The length of time for the noncompete could also very, and would typically be 1 - 3 years for someone who'd been an owner of that franchise location.