I love GNU/Linux but after many years and forks It still lacks some usability features.
Ubuntu cooks a very interesting operative system because it isn't targeted only for geeks but for people, obviously these suggestions aren't Ubuntu only but involve many communities and people which cooperate to improve this wonderful operative system.
Usability, coherence and powerusers support
GNU/Linux chose to copy from Unix and Windows, which isn't bad if the implementation is smart, but sometimes you have to break something if you want implement a feature correctly.
Cut-and-paste shortcut on Linux is CTRL+C and CTRL+V everywhere but the terminal which is CTR+⇧+C CTRL+⇧+v. In OSX the CTRL+C is used to stop the applications in the terminal (as an ol' school UNIX boy and Super+C (⌘+C) to copy everywhere)
Nowdays all web browsers have tabs and everywhere you can close a tab with middle click (clicking the wheel), but since 2007 this features have been reported with a lot duplicates and it has been closed but not resolved :(
If you want and autowrap console, you have use an hack :(
I appreciate to see lately Ubuntu in the supermarkets, which is GNU/Linux and not Android or Linpus OS, but with Asus and Dell exception, it isn't a real PC alternative OS. A very annoying behavior is that the Ubuntu version sold is outdated and the newer Ubuntu versions aren't 100% compatible or at least certificated for Ubuntu. I hate abandonware.
More standardization, less hacks
There should be separation between the system apps and user apps, the use cases are simple:
It would be very usefull to many non-English languages.
UI is very important, but fragmentation is a cancer without a common base. There are a lot of libraries in common, among the most full-featured Desktop Environment, but it's not enough because there isn't a common plugin system and some third party extensions will have to be specific and duplicated to do the same feature.
Please don't reinvent the wheel, if you can.