I really dislike what it does to mouse input.
If I select something, it's mostly because I want to copy and paste it. I am very good about crediting where I collect my copy and paste segments from, I didn't need apture to put in references to the original article in every single one of my cut and paste buffers.
Sometimes I select so I can search. I want to conduct the search with my favored search engine. I don't want Apture conducting the search (poorly) with the intent of keeping me at the original site.
And sometimes I click or even select in a window just to leave a visual indicator of where I am so that when I scroll or drag a window around, I can find my place easier. I don't want apture windows popping up whenever I click or select anything. To quote the Simpson's the Internets do not work that way.
And there was no way to opt out of it short of using noscript or adblock or other technologies to strip it away.
So: don't invade my privacy, don't insert text into my cut and paste buffers, don't steal my search abilities, don't steal my mouse clicks, don't pop up windows, don't break my browser.
Apart from that, it was a real winner service for the websites, and not for their visitors