This might help you to reduce some common errors
that slow down the vba code

http://www.ozgrid.com/VBA/SpeedingUpVBACode.htm

Mitchell Williams wrote:

when i've been working on a lot of long macros the
computer slows down a lot. I heard that it is because
the buffer memory is full or something, could anyone
clarify this or give a solution? is there any way to
empty the memory after a macro is run?