It turns out that inserting popular images into your pages can boost traffic to your site fairly significantly - as a result of people performing image searches on Google Images.
Copyright and bandwidth issues can probably be largely avoided by using images URLs taken directly from other people's sites.
You might think the search engine would penalise the use of offsite images - but apparently Google Images doesn't do that - though other image search engines might.
The images don't have to be very big. So: if you want to you can do this:
Remember that using "helpful" alt/title text can help!
Of course the traffic this gets you might not be of the greatest quality. However, those with ad-driven pages may not care too much about that.
It's possible that Google might object to this on the grounds that you are abusing their search facility - but if you have the images on your page and are adding relavant "alt" text to them, you may well be helping them overall. If they want to "cure" their system, they can easily do so - by penalising off-site images.
I've tested this - and the traffic boost can sometimes be quite significant. However, the process seems rather unreliable - sometimes you get featured in the search results - but sometimes you don't.
I can't guarantee this "feature" will persist forever, but - for now - enjoy (and I don't just mean the epic boobs!)
Update 2012-01-06: Sure enough - this page now appears in the "recently popular" section - on this site's right hand sidebar - and has racked up quite a lot of hits.