Because the web isn't always as safe as we thought, 1 in 10 websites google searches has some sort of nasty in it (
http://news.bbc.co.uk/1/hi/technology/6645895.stm) and we can't always be sure of how safe our fav sites are, here is a nifty little tool I found and it even better because it's free!
McAfee Site Advisor is a free little web browser plug-in, It has a firefox and internet explorer plug-in (Not sure about others) and it install nicely, giving you a little green or silver or yellow or red button depending on the site your visiting.
http://www.siteadvisor.comHeres a couple of screenshots:
I use it on both Firefox and Internet Explorer,now I dont know what I did without it.
Remember, surf safely!