I used to have Google AdWords' show_ads.js on the list of external scripts to minify and it seemed to work OK for a while.
Today, I got a big gap at the top of my pages, due to an iframe named "google_ads_frame", which only went away after un-minifying the Google scripts.
My guess is that Google scripts are minified already, so I'm happy this way and this is mostly for people who may have the same problem.
However, as far as the WP-Minify plugin is concerned, I don't see a reason for anything to fail after minification. Even if a script is minified, I still want browsers to fetch it in a single request, so including it should be a good idea.