1)Split window.
Maybe i am a retard but i often miss the window when i want to split it. It would be more flexible if you could still change the active window when you use the tool.
2)Hotkeys in Infobox
Sometimes tools are not available in the menus, only with buttons, but there is no information on what are the hotkeys for these tools. Displaying the hotkey in the infobox would be helpful.
3) Camera List
There is no obvious way to guess wich camera is the active one. A list in the render panel would be really useful.
4) File extensions.
File extensions aren't automatically added for pictures, but they are for .blend files. It is not really consistant.
5) Hotkey indicator
There is a lot of functionality 'hidden' with modifiers keys. a good example is Ctrl-LMB to open Image navigator. It would help users if it was said in the header free space 'Use Ctrl, Shift, for additional options. So the user would know that there is additional behaviour. Header is not the best place, maybe the infobox would be less intrusive...
6)Save render
'Save image' Is a quite 'vague' tool. I personally made screenshot of my render because i didn't found how to save it. (then i read the doc

7)Select Mode
A quick way to change the selection mode (face/edge/vertex) would be a Ctrl-RMB on a vertex / edge / face, and it would automatically change the mode.