Currently you have a link at the top of each lobby to a download of the map file. Once the user gets this bsp file he/she then has to rummage through the steam directory tree trying to find the directory that it goes in.
But at this point, you already have a server running with the map loaded and fastdl enabled. So why not have a url that connects the user to the server instead, so that the map gets downloaded to the correct place completely automatically ? With fastdl enabled, this will probably still work even if you kick the user as soon as they connect, if for some reason you want the server to remain empty.
Not only would this make downloading easier, but users who already have the map could use the link to preload the map on their client, making joining the game much faster.
Similar reasoning applies to the idea of a tf2center map-pack - a server which cycled through the maps would be a lot more convenient.
