Bukkit

Support for CraftBukkit 1.2.5-R1.0

Supports arbitrary world heights.  Set your world height in server.properties Planetoids will fill it all! (Bukkit, however, still has a maximum height)

Supports multi-world management plugins now.  Simply change 'autocreateworld' in the Planetoids config to 'false', and follow the multi-world plugin's instructions, using Planetoids as your chunk generator.  You can also still use Planetoids as it was originally designed, letting it create its own world automatically, by leaving 'autocreateworld' set to 'true'.

Last time I checked, Bukkit still imposes a maximum height limit of 256.