I have 3 Microsoft opticals and have to say I despise the Intellipoint drivers. I can't tell you how many times it has either "forgotten" that my scroll button is assigned to "back". Either I have to change it back in the mouse options (easy enough), or it insists that it is already programmed to back and still brings up the scroll cursor when I press it. :| I'm thinking about going with Logitech just for better drivers.
I do have to agree, however, that the exchange is painless. I've had two Intellimouse Explorers go bad (only equipment on my computers to go bad, believe it or not), and they shipped replacements promptly.