Eric Lawrence has added a cool new feature to fiddler to visualize what is happening in your http traffic. Here's a snippet from the online fiddler help:

Timeline

The Timeline Tab shows the transfer timeline of selected HTTP Sessions.  NOTE: You should enable Streaming Mode for the highest accuracy in Timeline rendering.

The vertical line indicates the time to first byte of the server's response.
The green circle before the bar shows that a connection was reused; a red circle means that the connection was newly created.
The green circle after the bar shows that the server didn't send a Connection: close header; a red circle means that the server sent Connection: close.
The gray arrow icon indicates that the server's response was a redirect (302).  The red ! icon indicates that the server returned an error code (404).

timeline

How cool is that?!

Ed.