the problem is that the blender gui got a bit messy and inconsistent over the years. it's too inflexible (hard to extend) and doesn't cut it anymore for the very comprehensive, feature rich application blender has become.

there also are no customizable keyboard shortcuts and it's not customizable on the button level (you can't change buttons or place your own).

so 2.5 will certainly be a huge improvement but this doesn't mean that blender isn't great and very useful already. i still find blender's current gui better than the one of many other applications like max or truespace.