VirtualPenguin: May wanna write this in the first post.
Railroads DO NOT work in multiplayer period! No testing facilities, subways or anything is needed!
Placing them causes a memory leak in your client and riding a cart lags the hell out of everything, do not experiment do not place them, wait for a fix.
While you are at it check out the known bugs
PLEASE http://www.minecraftwiki.net/wiki/Known_bugs_in_Survival_Multiplayer Maybe a warning on in the MOTD? Otherwise it's really easy to - like me - just out of curiosity try and build rails, not knowing the severity of the deed.
Also, sorry for my 62 piece long railroad track. :o
I'll just leave it there since removal also causes trouble. D: I'll add a warning sign or two to the area.