My main beef with UI is the chat box. The chat box has multiple tabs that correspond to the different channels, such as group, clan, and local, tells, and alliance. The problem with this Runescape Gold is that it is becomes easy to miss messages.
Let's say you are in your group chat tab running around looking for trouble, and you run across another player and kill them.
Unfortunately, that player asked if he could join you and wanted to provide you with some valuable information, but you missed it because his text was under the local tab that you were not looking at because you were talking in group.
Unless you are paying careful attention to the various tabs, you are bound to miss a tell or message in another channel. You can however click and drag those tabs out to create new chat windows for that channel. This also means that having a different chat box for each channel can start to clutter up your screen.
I think the chat would be better served with multiple channels in the same tab, and leaving it up to the user to decide which channels they want to see in each tab.
Aventurine has stated that further revamping of chat is already in the works and will arrive shortly, so there is a good chance that this will be less of an issue very soon.