I’m currently looking at using XHProf to profile WordPress performance on our hosting. It’s the first time I’ve really looked at the call graph generated by XHProf. It’s a crazy data visualisation that lists all function calls, it’s probably only of any use if it’s projected on a large wall in high definition.
Click on the graphic to take a look at a larger version. It’s not full size as that was going to be something crazy like 10,000 pixels wide.