Hi there,
overall usability of Code::Blocks is already very(!) good, way better than Visual Studio in this regard. Only shortcoming is auto-complete, which I acknowledge is a very hard problem.
Nevertheless, the place where most gains in productivity can be gained is the thing a programmer spends most of his time with: writing code.
Here are a few suggestions that will close the gap from "very good" to "near optimal":
1. Often some rows need to be rearranged or swapped. Notepad++ offers shortcut
CTRL + SHIFT + UP/DOWN
Once used to it, it is VERY hard to live without

Having also support for moving multiple rows at once would be the icing on the cake.
2. Next to writing code, the second most important task is adapting project configuration. Buttons that allow this in a one-click operation for "properties..." and "build options..." are desperatively needed.
3. Double clicking is not working correctly if a dialog other than CB is currently having focus (this may be a bug). So if the focus is not on CB I need to click trice

Surely not the intention of the inventor.
4. An up to date source code formatter. There is this Astyle plugin but it's really outdated. But more importantly it doesn't support all formatting options that Astyle offers. But I admit demand is not that pressing as this behavior can be emulated by including Astyle as "external tools". Still it would be nice to have this built into the IDE in its full glory, since it's already partially there.
Best regards, ZenJu