This is a minecart station designed as a hybrid of Bleh's door booster design (description here and video tutorial here) and a water channel minecart holder (used in http://www.youtube.com/watch?v=9NR6gQ0CXpk). Its key advantage over all automated non-door-booster-based designs which I've seen so far is that it doesn't require any traveling empty minecarts, which suffer from weird behavior on server chunks. Thus, as far as I can tell, it works perfectly fine on multiplayer servers, it's automated, it doesn't have issues with minecarts moving weirdly when players exit, and it can robustly handle multiple people riding at once.
The reasons this design uses a water channel to store minecarts are:
[*:38o4e8oi]Multiple players can arrive at a station without any issues
[*:38o4e8oi]Once players arrive, they don't have to worry about destroying their minecart or about it moving where it shouldn't be (e.g. backwards on the track, like in http://www.youtube.com/watch?v=ElawRqMXnD4)
[*:38o4e8oi]A constant force must be applied on the minecarts so that there will always be a minecart pushed to the launch position; this can also be achieved with gravity on a diagonal reservoir, but that's not compact.
As pointed out in the video, the only issue I've found that it suffers is that players who jump in a minecart held up by the door can't jump out, or else they'll fall under it.
You can download a world map version of this station at http://localhostr.com/files/oyNGDWP/Minimal%20Station.zip if you want to poke around and see how it works.
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Minecart fanatic and steward of Foonetic's #xkcd-minecraft server's two-lane rail lines.