I am going to Bulgaria, but... I would choose to go to Poland if I had a choice. I don't, unless I want to wait until March 2011.
Poland has, at this point, a lot more people going through and giving feedback (positive) on this forum, so easy to find.
Bulgaria has from what can be made out, a limited number of people going there, and so far no-one from TIMS has been. We don't expect any "internationals" like ourselves to have the procedure in Bulgaria until the end of this month.
To my mind, Poland has more experience with this procedure than anywhere in the world, including Italy.
I don't believe the procedure is particularly risky - if I did I would not be going to Bulgaria. I am going to Bulgaria because I don't want to wait for the procedure, which I think IS risky because it involves a probable worsening of my MS.