Hi,
When I've used them the biggest problem is that they take up a lot of space on the breadboard, and some have a rubbish pin spacing. The circuits haven't behaved in an unusual way. I guess depending on the circuit in question it could have a "big" influence, after all, where avoidable - sockets, sil pins and adapter boards are all a bit of a no-no, aren't they? They add inductance, resistance and capacitance, so - without knowing - may be terrible for a high speed or very small signal (uV/nA) type of circuit.