I'm kind of surprised seeing people claim they notice it slows down their browsing. I even saw one person say it caused more slowdown than their real-time AV did. Heck, I think my browser actually runs a hair snappier sandboxed than it does outside of it. Possibly because of the isolation... nothing else is leeching onto it (or trying to). It does add 2 seconds to the boot time of my programs. I get those back, and then some by forgoing real-time scanning. Plus it's much easier on my HD. I'm running XP Pro SP3. Perhaps it runs differently on Vista/7?