Obviously you've never loaded one of the "aggressive" flash ads with a bunch of buttons and clickable crap built into the animation? Because I have seen one of those drag a 3GHz quad down to a crawl thanks to all the crap its trying to render being spread like the clap across a dozen CDNs, half of whom take forever and a day to respond or time out, which causes it to call the next CDN in its list...yeah sorry but the new ads are even nastier than you can imagine.
If you want to see it for yourself just surf some "mainstream" sites like CNN, AOL, Yahoo "News" and the like for a couple hours with no adblocking, just be sure to have an offline disc image so you can blast the OS and restore from images. Hell I used to use a VM at the shop to let an image get the latest drive bys to test various AVs and stay up to date on removal methods but not anymore, with the latest bloated mess called "interactive ads" I had to quit because even with a C2D doing nothing but running the VM those bastards would slam it so hard I'd be lucky if I could kill the VM, it would just redline the cores to the firewall, nasty shit. Maybe if I slapped in a C2Q and limited the VM to only 2 or 3 cores I could do it again but frankly articles like this only prove my theory correct, back any precious memories, nuke the OS, and make sure they have a choice of browsers with ABP loaded into all of them.
Oh and just FYI since insisting that my customers only use browsers I've preloaded with ABP? I've watched infections disappear, even my most clueless click happy customers only have to call me for hardware or networking issues. Of course it turned out just as I told my clueless former boss it would, because I'm "the guy that builds PCs so they don't mess up" I get referrals up the ying yang so I don't have to worry about repeat business, they are happy to tell everybody and their dog the ONLY place they should get a PC fixed or have one worked on is from/by me.