If you are using it to test desktop software with WPF controls I feel your pain. The problem for us is with them is there are soooo many child objects it can take minutes for TC to iterate through them all. WPF has a ridiculous amount of container hierarchy. Actually though, any time there are a ton of child objects it can take a long time.
When the properties finally display how many child objects does it reflect? We have a tree control with thousands of children. It takes several minutes for the Object Spy to return anything when you select something in that tree.