I have the same thing... I believe its the hydroboost. Every now and again it catches... the reason I know its the hydroboost (in my situation) is that one time it hung at center. It was doing it routinely for about three months, with the last time being when it hung at center... it has been fine since Thanksgiving.
You can also hear the PS pump complaining as you fight the wheel... but its not the pump as the brakes work fine.
I'm thinking that there's a piece of dirt somewhere in the hydroboost, not allowing something to seal/release... since it seems to have flushed out now. On a side note, I had the same thing happen on my 99, only it was the brakes that stuck.
I'm considering a Magnefine filter for the steering system, but with 235k; its probably polishing a turd.
On edit: this is not a jerking steering wheel (like a seizing joint), but the steering wheel actual binds at some point (a left turn in my case) and literally refuses to return to center. It always happens near idle, and only shortly after start up (hot/cold doesn't matter). I'm not small by any means, and I can barely force the wheel in the opposite direction when it seizes... to most people, it would essential be frozen/stuck in place. A quick (and against all normal reactions) jerk in the same direction its hung will always free it when it happens to me. And further, there is a force against you when trying to return to "center"... this isn't just a loss of PS assist.