Last night, while surfing around for some medical information, one of the sites I stumbled upon through Google's search results tried to install a Trojan on my computer! This was surprising, seeing as I was using Firefox 3.6 with AdBlock turned on. Thankfully, Microsoft Security Essentials saved the day, alerting me to the fact that a nefarious application was trying to install itself. The tool caught the incursion, alerted me, and successfully removed it from my system. I then did a full scan and it found no other problems.
I've read that drive-by attacks like this are becoming more common, but until now I hadn't ever been affected. Several of my plug-ins were outdated, so I updated them, though I'm not certain any of them were involved in this attack (Java never loaded, and there was no embedded media on the site).
That being said, make sure to surf with protection; there's some nasty stuff out there.