Maybe I didn't understand the question but...

     I'd be careful when using a cap to tap off of line voltage.

     When I design anything I always think about stray bandwidth - do I
     have more than I need?  If so, how are the various impedances in my
     circuit going to respond to it?

     Ideally, any supply that takes line voltage and steps it down would
     limit the bandwidth to as low as your circuit could tolerate (it would
     be a low pass filter).  By limiting the bandwidth you'd cut down the
     RF, ESD, and transient-type problems in your circuit.

     With a series cap as the voltage dropping element you'd have a high
     pass filter - the higher the frequency - the easier it would conduct.
     ESD, RF, Line spikes would all eat you alive unless you put a low-pass
     filter after the cap.

     It doesn't seem safe.

     ... just my impression...

     Jon Bertrand
     jonb@cirris.com