but when it comes to searching for adhoc- stuff across all groups it baffles me.
I just put a search string in and search. If the search topic isn't too broad, I don't hit 2000 hits. I use watch lists for searches I want to do periodically, that I want to collect so I can look at them later. I use the search tab primarily for stuff I may have heard about somewhere. If I want to look inside specific groups that I'm subscribed too, I select the group topic before I search so the search engine only looks in those groups. If I know the files are relatively large I set a minimum file size which tends to filter out the spam. I treat it like google.
I'm not getting the 2000-10,000 issue. Are you planning on adding all 10,000 to the download list?
Old results are static and unchanging. It's not like if you search today and see something, you'll see something different in the old results tomorrow. Only the new results change, then they too become static. Nothing is ever added to the list from the past. So, if you collect up 10,000 results, You download the 100 things you like, it's pretty much pointless to then generate the list again because nothing will have changed in the old results. You'll see the same 10,000 you saw before plus new posts that happened since the last search so, you probably don't have to collect more than the defaults except for the first time you search for a particular topic.