There are lot of friends of mine who complained that IE 8 was bit slow for them even if I had convinced them that if you love IE ,IE 8 is best of all its previous versions. On further checking on their IE installation I accidentally find that the slowness of IE 8 was because of Extensions or Addons.
How did I measure the load time of Addons ? I did not, IE 8 does it on its own. Go to Tools > manage Addons and you would see list of addons. The right pane gives lot of details which includes the Load Time column.
This should be the first place to check out,in case your IE 8 is loading slow. If you find any addon loading time to be higher,disable it and see if IE loads faster than before. If yes either you need to update the Addon or just discard to find an alternate which doesn’t make your browser slow.