I took a quick look at the bandwidth and latency graph for my home DSL line -- Evolution's misbehaviour is fairly obvious on it.
I started the 'new and improved' Evolution at about 7pm on the first day, and it spent about two hours downloading headers before it fell into a pattern of thrashing the link once every few minutes, downloading the flags of every mail in the folders it was checking.
Note that this was after I'd applied some of my own fixes to it, to make it check mail only in active folders rather than in all folders. Without that, the problem would be about an order of magnitude worse, because it would do have been downloading flags for about 3 years worth of historical archives each time, rather than only for mails in the currently active folders. Out of the box, Evolution would probably have given me a solid mass of green in the graph.
On the afternoon of second day, you can see that I stopped it -- that was when I was playing with the patch which I then submitted to Red Hat bug #183219. After an hour or two I gave up on pursuing that approach myself and restarted the original -- you can quite clearly see when that happened too. I looked at the bandwidth graph and then killed Evolution at around 12:45 on the third day, and then the line usage went back to normal.
I'm now looking at kmail; once I add the facility for accessing an IMAP server over SSH, it should do quite well as a replacement. In fact, if I'm going to start using KDE programs I might as well just switch over to KDE wholesale -- it'll save me from the constant temptation to kill someone when I have to deal with the insane GNOME file dialog box.