Yahoo! Pipes is seriously addictive. I've been up all night playing with it, when I should have been out drinking with friends. Social web indeed.
Anyways, this is what I've come up with - the Pipe takes a Last.Fm user name, grabs the recent tracks feed, does a "content analysis" on the tracks, and uses the output of this to grab a bunch of pics from Flickr. Theeeen, I use the JSON output of this new feed and fetch it in a Greasemonkey script. The Greasemonkey script fires when you visit people on Last.Fm, and adds the images below the user's "Recent Tracks" listings. Ok?
Trust me, it's pretty cool. The results of searching Flickr based on the content analysis of track names can be pretty random - so you get some results that are very fitting, while others are totally unrelated. Which is the best bit. If you mouseover the images you can see the photo's title - click it to load the Flickr page.
To add this super feature to your Last.Fm experience, just install the Last.Fm - Add Flickr Photos greasemonkey script and head on over to Last.Fm.
If you want to see (and clone and tweak) the pipe I used to create the feed then check it out on my Yahoo! Pipes page