Can I treat the pogoplug just like the sheeva or is it crippled to make it "pogo-distro only"?
You can, but the PogoPlug Pink has "only" 256MB Ram and 128MB internal Flash-Memory.
But thats more Ram than the Dockstar and if you are using a USB-Device as Boot-/Root-Device
it can be very useful.
A PogoPlug can also be reconfigurated to debian ( search for Jeff Doozan and Pogoplug ).
Here you can compare the Plugs: