It would be great to be able to use multiple segments at once. Many times I will have a segment based on page type and another based on device type. It would be awesome to be able to apply them both to the same report in an "AND" function. If you want to be fancy, it would be great if we could choose if we want it to be an "AND" or and "OR." This would of course require the backend ability to create a segment with AND's and OR's which is also a much needed improvement.