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Slows down search pages.
LinkScanner is okay for regular browsing, I guess, but it slows down search pages something awful--I'm guessing because, naturally, the page consists mostly of links. When I had it enabled, every time I googled something I ended up having to wait an excruciatingly long time for LinkScanner so the page could finish loading. I finally got fed up and disabled it. Instead I started using the WOT add-on for Firefox, which from my initial impression probably isn't quite as accurate, but which accomplishes essentially the same thing without slowing down searches much.
Pros: It's not made by Symantec.
Tells you when a site is sketchy.
Cons: Causes search pages to load with the lightning swiftness of a heavily sedated sloth in wet cement.
If you download it as a standalone application, it will infect your browser with Yahoo toolbar, the athlete's foot of the internet.