Actually that was Snap, ASK seems to be a little less aggressive.
Keep in mind that making screen shots is a slow process and they're making screen shots for many millions of websites. I get about 100K page impressions per day, not all are AdSense impressions though, but you can see it would be hard for me to easily tell the impact of these activities while a smaller site might notice right away. However, I've seen various IPs from Snap's screen shot tool [webmasterworld.com] ask for a couple of hundred pages a day for my site.
I never really thought this was a newsworthy item until I noticed more and more sites making screen shots and I figured if Google were actually filtering those sources (Ask, Snap, etc.) you should see PSA's on the screen shots and not real AdSense ads which clearly isn't the case.
As a matter of fact, I myself use a Windows-based tool called WebShot that uses MSIE to make screen shots. Using that tool I recently made about 30K screen shots for my directory site and they show AdSense if it's page. You wouldn't even know a screen shot had been taken because the WebShot tool drives MSIE to take the actual screen shots.
There are a lot of services that make thumb shots like WebSnapr and Thumbshots and these services have to update those images, as well as I'll have to update my images, so it's escalating a bit.
I wouldn't say that this activity is so large it's a problem for AdSense yet but I'm wondering if they're having any overall impact and what, if anything, Google is doing to filter out the obvious sources of this activity from our stats.