Users of Viewport Switcher > Desktop-based Viewport Switching should be aware that there are issues with that plugin & the current 3.8+ gtk that will affect scrolling.
Whether affected depends on use, most obvious will be scrolling in large files with gedit & long package lists in synaptic.
This first was seen with a late committ to gtk in raring, the issue was 'fixed' by reverting the commit in 13.04.
In 13.10 the change is now part of gtk so has returned.
Initially I couldn't see what was causing this to occur in unity sessions, finally tracked down to the bindings for Desktop-based Viewport Switching. If they are set scrolling will be affected. (also affects gnome-flashback w/compiz
Current bug on poor scrolling - 1184159
Also have found that on a laptop if a usb mouse is attached the there is no scrolling at all with that mouse in numerous windows - 1200829
While the bug was orig. on gtk it's more likely now only to be fixed in compiz. With the current state of bug fixing in compiz it's quite likely this will not be fixed in 13.10 or anytime in near future.
In that case, if affected, then you'll need to disable the bindings in Desktop-basedViewport Switching or revert the gtk commit. Seeing as though I use 'scroll on desktop' the later is the only acceptable option here till fixed.
So in meantime will provide gtk packages in ppa with commit reverted, have not yet seen any ill effects of doing so (& was never affected by bug that caused the commit in the first place..