WARNING: This post is probably incoherent, and very rambling.
For the MG download thing, I was going to code up a big map upload system. I gave up. The general idea was, it would track maps and files seperatly, so I would say I made a map called ATCS, and then I could upload lots of files attached to it, and it would only show the one marked as the latest in the list, while leaving the others downloadable. (Version number spam is annoying).
It should also check your maps are legit, should be map-name*.pk3, the map-name bit shouldn't conflict with someone else's map, should check for a (valid??) bsp, make sure no QVM's/other stuff etc.
When uploading it should auto-extract the levelshot, and have an option for them to upload sources and other files with it, and licence etc etc.
Should also track stats from downloads, how many and if auto-download or people on the site.
Anyone should be able to rate them, and leave comments, then there should be a team of reviewer like people who can leave formal reviews and can promote other peoples stuffs to being a proper review, so anyone can write one and if its well written it gets there.
Comments and reviews etc should be vote-able them selves, so spam sinks and good stuff rises.
Comments should be tied to both the map and the file, so when looking at the latest version of a map I see reviews for the beta, but it says its an old review in big letters.
The whole thing should be searchable / sortable for ease of finding stuffs. Nice ajax form please
Should also be able to tag them, and get a tag-cloud or whatever.
Default maps should be marked.
It would be totaly awesome if it could tie into the master servers game stats thing to be able to say how often its been played and on which servers, and a rough guess as to which servers have it in rotation.
IMO new mappers should have to be checked before being OK'd, but have a large-ish team able to do it, (same as reviewers??) and be able to mark someone as trusted, so once you've produced a "real" map, you can just upload them and we assume you're not a spammer/retard.
Either offer http downloads for servers (would need mod support etc), or have a way that those of us who do can easyly mirror all new uploads.
Should also provide a md5sums file so we can make sure there all OK.
Be nice if all authentication can be tied into the forums, single signon etc.