First load of 'optical' mice were like that - I had one
Many was the time I couldn't point it in the correct direction. It had a ball and an IR reciever.
Only real problem with wireless keyboards are:
a. sometimes they broadcast a bit further than expected (so people in the next room using one can get your signals)
b. some have problems in that they don't like having several keys pressed simultaneously/a key pressed at the same time a mouse movement was taking place (so you couldn't 'shift' click)
Only problems with wireless mice are:
a. Batteries always die at awkward moments
b. reaction time can be a bit slower when you play online games.