For persons like me who spend day in and day out using computers, ergonomics is a MUST HAVE. If one does not pay enough attention to these issues, you will end up with RSI. Mouse, Keyboards and Monitors are primary tools that should adhere to ergonomics.
I have a DELL D620 at workplace and the DELL Mouse that comes with the laptop is quite huge and heavy to use. I always end the day with a slight niggling pain the hand.
On diagnosing that heavy mouse is the cause for the pain, I changed it to Logitech Optical Mouse. It costs around Rs 400/- in the market and it is pretty light to use.