After searching, with all types enabled, using a term I knew a fellow user would have hits for, I was returned with _some_ matching hits but not all of them for that user (confirmed after browsing the user's file list). It wasn't until I reduced the search types to just one that I then received the match I was originally looking for.

Is there a per-user limit on the number of matching hits returned to an individual search? If I was to guess, looking at a number of result lists, it appears the maximum number of hits per user is limited to about 40-ish - but there's no science behind that estimate.

Yes, I've also noticed that the search hits limit is indeed 40 per user, probably to keep network overhead down.