I experienced laggy bad scrolling on the Nexus 7 and it turns out the problem was other applications running on the device. I rarely have the problem but if I do, I just swipe off some old apps and it speeds right back up. It's probably just one app but I haven't bothered to figure out which.

I moved off of Chrome as my default browser and now use Dolphin with Jetpack -- no only is it faster but it generally works better for pinching and zooming.