Similar problems down here and followed much of Milo's advice which, in part, helped.
Goto control panel<>programs and features (Ok so I am using Win7) and review and get rid of any programs you do not use or have not used for considerable time. You may find some of these are puting in `add on' which are interferring with IE operation.
Similarly, review all the `add on' from ALL sources and disable those not needed or used. Maybe disable all and enable them one by one may help eliminate a problem one.
Adddtionally, got System Configuration<>Startup tab and go through all the items in the start up list. Disable as many as possible or set for a delay startup; again some of these programs interfere with or interfere with IE.
I have and use Download Accelerator from Speedbit and it puts all sort of bits and pieces throughout the computer or IE (including it's bloody search engine) and eliminating some of these improved performance but the problem still is present from time to time.
Still looking but hope this assists.