If you use Internet Explorer 7, but would like some of the many features in popular addons for Firefox (like adblocking, greasemonkey scripting, etc.), give IE Pro a try. It is still in beta, but already adds a lot of features to IE as this feature list from the IE Pro web site demonstrates:
* Easier Tab Management
* AD Blocker
* Super Drag and Drop
* Mouse Gesture
* Save Page to Image
* Proxy Switcher
* Crash Recovery
* Greasymonkey alike User Script