It often happens that I need to move a task from one user story to another (for instance when a whole user story emerges out of something we thought would be simple). Right now it's quite onerous to move a task to another user story -- I count 7 clicks to go into the task detail, click the plus button (which btw doesn't give the affordance of being a "change user story" button), find the user story from a huge list, select it, save the task, etc.

Instead there should be a simple dropdown menu item on the task saying "Move To Story" that pops up a user story search dialog and allows you to change it. Also, you should be able to drag a task from one user story to another to change its association (although the "Move To Story" is still required because often when I'm moving tasks it's to stories that are on the backlog).