Bukkit

I tried your plugin before giving PortalStick another go, and have a suggestion that would make this a lot better:

In portalstick, it only replaces existing blocks on the same layer - it doesn't add blocks like yours does (and thus makes it harder to drop in the portal)

Also portalstick seems to have some "correcting" for floor portals, if you land on the border around a portal at a hard enough impact/velocity, it will still register you as going through the portal.