Although Bukkit is very stable, we use it on mono.soho.on.net, we tried the multi-world support for nether (and other worlds) and found it to be very unstable. The chunk where the return portal is would often unload. So players would end up falling into the void on return.
The only set-up that's reliable so far is Raphfrk's Server Port. But that requires multiple Bukkit servers to be run. We've run that successfully for a number of months (it's down at the moment as Raph's rewriting it from scratch). Running multiple servers is actually better, because you can take advantage of multiple threads running on separate cores (or even separate virtual machines, or separate hardware).
I don't think the experimental nature of these plugins are compatible with Node's policies, however.
The Centre of the Australian Minecraft community: minecraft.net.au