nUI Plus has been working fine since the 4.3 patch if I load out of date addons except for the fact that the latency indicator constantly shows 0 ms. This may not be a huge issue for most people, but I only have a dialup connection and no other internet alternative, so it is a vital tool in determining causes with lag issues, as in whether redialing my connection will help or if I am just experiencing issues caused by large crowds of other players or mobs.
I have tried it on a PC running Windows XP and three separate Macs running various versions of the OS X 10.6 operating system.
I am sure I did try it on the PC, even though that isn't my normal WoW computer, but I just tried it again and you're right. It shows latency. I believe the only explanation I have for not seeing it before on the PC is because I must have been drunk.