The XML-RPC interface to PyCS has been plagued with speed problems since day one, but only on this server, not on my development workstation. This hasn't caused any obvious trouble until now, however, when people are trying to upstream large-ish HTML files after running Dave's weblogNeighborhood tool.
I think the problem is fixed now - PyCS was using Debian's default version of Python, which unfortunately doesn't seem to include any of the fast XML parsers.
The solution? Upgrade to Python 2.2 and install python-xml2.2, the new, improved XML library. Now upstreaming to PyCS is much faster and should no longer stall the server like before. I'm testing it out now.