Get a decent one.
I have these new 2.4GHz wireless connection ones.
One little tiny USB plug connects both mouse and keyboard to PC, if battery is dyng etc, it doesn't lock on one key, signal just drops out instead, perfect. I can easily move my keyboard and mouse around and feel no difference in response time compared to wired.
Response time is only like 5ms different, and most screens have far above that anyway :P
If you have an old wired mouse it'll be slower than the new average wireless ones ^^