Sorry about that portal issue. I have a feeling it's a problem with the MyWorlds plugin. There are various ways around it, but it seems a bit pointless to try and fix it given that the mod itself has to be upgraded when 1.7 comes out. Until then, just use home to get back from the end. I doubt it will be much longer before Bukkit 1.7 is out.

For the Iron Farm situation, another option would be to use another world to store the thing. I can set the spawn chunks in any additional world to be loaded just like they are in the main world. If you want, I could make a small permanent world just for the Iron Farm and leave it loaded. We could then put a portal to it anyplace in the City, thus providing easy and permanent access to the farm without having to fit it into the existing spawn area. That said, if you can fit it in without it looking like crap, that's fine too.