I went home and did a little bit of research and found that all is not that rosy, including this report on Microsoft's wireless keyboard. Even banks are at risk.
Logitech representatives say their RF wireless keyboards scramble their security codes each time the computer boots up. With more than 4000 possible combinations in the Logitech models, it's unlikely (though still possible) that someone else's nearby receiver would pick up your radio signals. HP is increasing the number of security codes for its keyboards from 2 to 256. (Source: PC World)But how exactly does Logitech fare? Perhaps, not very good.
I am staying away from wireless keyboards for now.