I use a wireless keyboard with my Macbook pro. After a little more than one year of use several keys started malfunctioning (not in some line). I had to press them really hard to still let them work. What i did as a solution is:
* i turned the keyboard off with the little switch on the back
* Held it upside down (keys facing the floor)
* Rubbed over the keys
* dropped it a few times on the keys from a hight of approximately 8 centimetres (3 inch?)
* noticed that some sand, dust and little hairs ended up on the table
* turned keyboard on again
* After that keyboard works fine again
* realised that my cats regularly walk over the table (and keyboard), and they do bring sand in the house ;-)