I haven't tried this out yet, have relied on the built-in tracing in WSE, but the tool looks like it could be very helpful. Live tracing of in/outbound WSE 2.0 messages.

Latest tool to use with WSE 2.0.

Previous version of the tool with more info about it.

Newest version of the tool, for WSE 3.0 (beta)

How I got here in the first place, Julie Lerman's blog.