Most annoying thing for me, the aircraft selection.

Firstly it takes ages to load, then I always use the mousewheel to scroll in all games/apps and Windows. So my natural action is to scroll down using the mousewheel, only it changes the top left aircraft manufacturer menu because that is where it always defaults to. I have to change it back to "All", wait ages for it all to load up then click one of the aircraft to scroll. Yes I do like to look through what I have installed rather than go straight to something.

It's a small thing, but small things can be very annoying.