I have only noticed the Find Results collection and its behaviour recently. I've found that while I'm able to copy the collection to give me a more permanent result of that search, it's unfortunately limited to only the results that it matched at the time it was run.
Ideally, I'd like to be able to define a search, attach it to a specific file collection and then have it run every time that collection is open. This would let me set up a number of shallow searches across my drives, such as a collection containing everything downloaded over the past 7 days, or the projects I've modified in the last 3 etc.
I know that I should probably just wait for WinFS - although I've yet to be convinced over Vista - but I thought I'd suggest it anyway, just in case this functionality could be neatly constructed out of the existing components of DOpus.