Not quiet sure,where to suggest this,but i'd just like to be able to do Transparent Buttons instead of uploading an actual picture and put the button in the same place.
This has been suggested in the requested features a while back but they still haven't added it. I've been waiting for this myself :/
In response to MDC
I *think* I remember Lummox JR mentioning at one point that supporting the PNG alpha channel for button images (and presumably other controls) may be a possibility, although I don't know how high a priority it is. It would be a great feature.