AV software bothers me so much. It's not just that it's generally ineffective. It's that when you bother dissecting it, you usually find it make users less safe (e.g. non ASLR/NX injected binaries, dangerous root certs, vulnerable hooks and format handlers, etc.). That said, Avast has caused me unique pain, and my personal experience correlates with the author's.
Chrome's sandbox blocks all access to system resources, so it's a very bad idea to inject hooks into our sandboxed processes, because they usually just break. So, we often have to use the sandbox's loader hooking mechanism to block third-party DLL hooks that are known to cause crashes (ie. "security" software and other process-hooking utilities). Of course, Avast shows up regularly as a crasher, so eventually I added their DLLs to the block-list and then tried to start Chrome.
So, imagine my surprise when blocking the offending Avast DLLs breaks Chrome by preventing all content--even internal content--from loading. I dig into it a bit more and find that Avast is hanging all our sandboxed processes, because their system-level hooking is so invasive that they won't let any process run if their injected DLL hooks don't attach. At that point I was forced to give up, because there's not much you can reasonably do against such recklessly invasive software already present on the system. It's really not very different from malware.