Are rotating stations realistic ?

This year (2010) the russians will send their Leonov ship to Jupiter to
recover the Discovery ship (the one with HAL in it). This ship appears
to have a fixed spinal structure, and a rotating structure at about midship.

Babylon 5, to be built in the 23rd century, will have a rotating central
cylinder, but a fixed structure that will hold solar arrays for instance.


Are such structures realistic ? Is it possible to maintain proper
attitude/orientation of the fixed structure attached to a rotating one ?

Are airtight rotating joints allowing movement from pressurized rotating
living space to fixed living space possible ?

More importantly, is it realistic to have a smoothly rotating structure
despite imperfect mass distribution in the rotating structrure ?

In a Babylon 5 scenario, an imbalance at just one end of the cylinder
would have very interesting side effects on the whole structure.


Or is balance easily achievable with some accelerometres couples to
powerful water pumps to shift counterweights quickly enough to make such
imbalances imperceptible to occupants ?