To those of you, who voted down that I'd think about a way for making it possible to see fancyboxes that do not pop up automatically, I have good news: I've decided not to allow No FancyBox show any fancyboxes. If you want to see the target image (or whatever is in it), you can right-click and choose "Open in New Window" or "Open in New Tab". :)
Fancybox itself doesn't use much CPU, but its probably the Flash/Video ads being served in the Fancybox that are taking up a lot of the CPU. Fancybox is extremely common on portfolio sites, and there are many legitimate uses. I haven't seen a lot of ads being served up in Fancybox (which is just one specific version of the Lightbox effect). This blocker seems like it would interfere more than it would help.
I have been happily using FancyBox for my portfolio website :( I had no idea anyone had negative feelings about it. It's the easiest and most versatile lightbox I've found. Can anyone recommend another if people are going to start blocking it?