A few small things that have bothered me since launch.
As someone who plays both HoN and LoL I'm always thrown for a loop when I get into a LoL match and forget the game doesn't have this. In HoN you have the option of enabling a colored glow around enemy and friendly players, making it easier to see who is on what side when a team fight become clouded with ability effects. The game already sort of has this too. Mousing over a friendly or enemy player causes them to glow their respective color, why cant I constantly enable this?
UI Placement / UI Position Saves
In LoL almost every aspect of the interface is movable around the screen, why then does the game not save where you put each element between matches? If your a widescreen user its twice as bad, as everything defaults to being slightly off center.
Its been said to death but I'll say it again.
LoL needs this badly. The entire game is based around moving your character with one hand and attacking with another. In a fast paced match having to find cover so you can take the time to type out an important message (Incoming mid, Missing Shaco, watch top brush, etc.) is not only implausible its unacceptable. Playing pre-mades with friends helps alleviate this problem with the use of external clients yet nobody has an endless supply of friends who are always on or willing to play at the exact time you want to. For a game that tries so hard to be considered competitive it surprises that this isn't on the top of their to do list.