MultiMC is doing a thing for mod installation: http://multimc.org/posts/introducing-quickmods.html
It looks like mod authors create a url for a .json file that contains information about the mod and a download (or adfly) link.
Ooh shiny. Great for people who like constantly reconstructing mod packs or for iterating a pack.
Might even allow people to automatically update mods and mod packs, just by launching the client.
(This reminds me of a system Mekanism came up with a few months ago that allowed you to download the newest version of the mod from within Minecraft. You'd have to relaunch to get the new version, but there was no download link chasing, googling, adf.ly-ing, or browsing to find the new file.)