I personally like the conversation-based private threads much better than simply individual PMs. Here are two improvements I'd love to see:
1) An "advanced" search page. Yes, you can search now (and that is a godsend compared to before), but I'd really like to be able to search the title (versus post text), users included in the conversation, and for messages with attachments. A date range would be helpful also (I have PMs on my forum going back to 2002).
2) When viewing a list of conversations, the ability to sort on the various columns would make finding conversations easier. Sorting on the Starter, Topic, To, and date of Last Message would be helpful. And clicking again on the column to reverse the sort, icing on the cake. I'd actually like to see this in other places on the forum as well, but starting here would be nice. Oddly, you can sort on the "To" column now, but none of the others. Hmmmm, that doesn't actually seem to work.
..Al