I clear my cache alot, and I have my browser set to private.  So, everything is new when I start up a new browser search. 
My computer is hitting the 6 year mark without a hiccup.  The flash memory is full, and I need to order new memory for it.  I recently cleared all my photos, and important stuff over to a external HD.  This freed up the main HD for everyday things, and sped things up a bit.