There is also an acknowledged problem with AIS firewall and uTorrent that maybe causing your issue.
http://forum.avast.com/index.php?topic=71639.msg600696#msg600696Vlk posts back at end of Feb 2011 that there trying to fix the problem but as of now still nothing has changed.
I have this exact same issue and to stop the system from grinding to a halt when using utorrent at times you have
to uninstall the AIS firewall module.
In my case I did a fair bit of testing and I only have the system slowdown issues when running uTorrent when
the AIS firewall module is installed. When AIS firewall module is uninstalled I have absolutely no problems with
uTorrent and system slowdowns. Just means I have to use the Win7 firewall.
You can try a quick test next time you get the system slowdown with uTorrent, try stopping the AIS firewall and
see if it fixes the problem. It's only a temp fix and doesn't always work well.
I hope they can fix this problem soon as I payed for software that I can't fully use whilst other firewall/virus
solutions don't have this problem.