This is why I dislike AutoArchive. The user delegates the clean-up responsibility to a tool that does no filtering; it saves everything. Receipts, jokes, Out of Office replies, etc. I can't force the user to not copy each and every item into his .PST, but I'm not going to enable a tool to move everything en masse.

As to .PST size slowing Outlook down, what difference does it make whether it's the default .PST that's huge or the user-created one(s)? Most of the slow-downs I've seen are due more to the user-created .PSTs than their default destination.