Having done a lot of googling for art before coming to Danbooru (like many of us, I imagine), I'd like to say that I'm certain we get better results still here than on a search engine. Danbooru has quality control/standards, and there are no 404s or reposts when looking for images via Danbooru, so even without multi-tagged posts, Danbooru is still a great resource, far better than most search engines. Well, for searching for anime related things only, of course (not a suggestion Danbooru should expand its theme/purpose).
I already miss multi-tagged searching, but at the same time, if that's necessary, I understand. If the strain really is in especially long chains of keywords in searches, I'd really appreciate being search even just two or three keywords at a time. Though I don't think I've ever searched more than that many anyway.
Searching for simply two would allow for finding wallpapers for certain series, animated gifs of certain characters, parodies involving a given series, certain couples of characters, or a character in a single specific context, and that would be really nice. I know that it's one step beyond the basic functioning of Danbooru, effectively doubling what users could search compared to no multi-tagged searches, but I don't think it's an immense luxury. Then again, I don't have access to the server data.
However, there are some people who do have privledged accounts that, that as far as I can tell don't do anything on the site. Maybe they tag and change ratings; I don't know. Profiles don't keep track of that, and I'm not asking for Danbooru to keep track of it anyway, but it's true that some people don't have more than a couple uploads, no wiki edits, no notes, few comments and forum posts (though I'd rather there be few than many unecessary ones), and a lot of favorites. I know I shouldn't say something like that and not back it up, but I don't really want to point fingers either, especially not knowing if they add tags and/or edit ratings.
But some portion of them are probably leeching, and I can only imagine they happened to have a friend already had a privileged account. I'm glad for them and all, but it does partially defeat the encouragement to contribute to the site. Maybe there should be some bare minimum level of uploads, notes, or wiki edits to be eligible to be invited for a privileged account at all? Note that I say 'or,' not 'and,' since, for instance, people would have a hard time meeting a requirement for notes if they didn't know Japanese. Anyone who already has a privileged account who wouldn't meet the requirement could simply be grandfathered in. I don't know what base line value would be reasonable, admittedly.
The only major problems I can see with that are that it's another thing for Albert to do, and another thing for the servers to do too (and I'm not making light of those either). I wouldn't expect it to be that big a server drain; invites must be much more scarce than searches, after all. The server already keeps track of these statistics, so how bad could it be to check some of them before inviting someone?
A possible lesser issue could be that some people might feel a sense of entitlement for a priviledged account the moment they reach those minimums, but they could just be reminded that they are minimums; it's not like people don't ocassionally come in the forums passive aggressively asking for privledges already. Another minor issue I could for see is people making bad edits, notes and uploads just to try and meet that minimum, but I'd like to hope people have more good sense than that.
If the minimum standard was just on uploads, then it's not like they could do anything too terrible; there's a post limit on normal members and mods do the job of approving uploads already (thanks guys ^^). It's not that hard to find images to contribute to danbooru, either; anyone can do it, you just have to expect to run into reposts.
Gah, I prattled on there; to anyone who bothered reading all that, thank you for your time.