I'm proposing some improvements to the way transitions work in Kdenlive, by making them work more like the ones in Sony Vegas.
Right now, in Kdenlive, to add a transition you have to put two clips onto separate layers on the timeline, right click on the transitions layer between them, select "Add Transition", and then click on one of the options. There's no reason why you should go through this many steps just to add a transition. Plus, the extra layers for transitions are an unnecessary waste of space.
In Vegas, trasitions are much more intuitive: A transition (crossfade by default) is added automatically wherever two clips on a single layer overlap. You can resize the transition simply by moving or resizing the involved clips. The transition will automatically disappear if you separate the clips. The transition's properties can be modified by right clicking on it and choosing an option from the menu. If you'd like to add a transition to the beginning or end of a single clip, just drag one of the corners. All of this works with video and audio clips alike.
Transitions are easier and faster to use in Vegas, and they don't take up any extra space.
I'll try to post some screenshots of Vegas later so you can see what I'm talking about. Also, if you'd like to try Vegas yourself, you can download a 30-day trial here: http://www.sonycreativesoftware.com/download/step2.asp?did=768