Mod idea: Add a keybind to put the player in 'flying mode', analogous to how pressing Control causes you to sprint if you don't want to double-tap W and some random mod doesn't eat that keypress event.
On that node, my irk: Mods that eat keypress events, so you can't have two different things in two different mods bound to the same key, even if there are no circumstances where both mods would ever actually act upon the keypress at once. For instance, in the appropriate pack, I'd like to bind the Clockwork Phase 1 temporal tool key, Redstone Arsenal empower tool key, the ProjectE release charge key, and the Thaumcraft wand focus switch key all to F, since they all do similar things and only do those things when I'm holding an item from that particular mod in my hand. But, if I try it, two or three of them will inevitably not work.
Heck, even if there was some way to enable a thing that would tell me which mod is eating any particular keypress event, I'd be much happier. Just last week, I had to disable seven or eight different keybinds that defaulted to my Control key in order to make the vanilla Control-to-Sprint thing work. Some of them looked like they'd be useful to have on Control in the future, but there was just no way to find which one (or ones) was breaking my sprint key without going through them one by one.