It is good idea but not really killer feature. If you have visual editor it is right format to store UI but defining UI in XML is not easier than defining UI in C. Instead of handling coding errors introduced in C language you are handling syntatical errors in XML... but it is very neat idea nevertheless and I would like to try that for MUI, too.
I dont know why any UI system should have integrated logging system unless this mean getting some useful data about errors in UI definition/logic.
No matter what is talking about you always have negative words about it O_o :-(
