I also have been having this 100% CPU load problem with avast. I was using Avast home free version and was experiencing the problem but was not sure what was going on, yesterday I upgraded to the internet security version of Avast 5 and now the problem is even worse. I have a cor2duo 2.4 with 4 gig of memory, plenty of HS space etc. I really notice it when I have Agent news reader running downloading bodies. Doing anything else on the computer is pretty useless. So I tried turning off shields for 10 minutes and then I couldn't access Avast anylonger, also my mail program no longer could access my mail and the news reader could no longer connect with any server. I could NOT open avast in order to get it going again, thus I had to resort to a reboot.
I'm not a happy camper now with this issue. Anyone else notice this HIGH CPU consumption?