I am in a process of selling my Rancilio Silvia and am looking for some guidance on how to prepare it for shipping. Do I have to drain the boiler?
Any help will be greatly appreciated.

I would, for the simple fact that if it starts leaking the post office/shipping people will probably open it to see if it's something hazardous/etc.

As for how to pack it, I have no idea. Big sturdy box, lots of bubble wrap and paper. I always over pack things. Damage sucks.

See Shipping Silvia (CG), Boiler Draining Instructions (WLL), and a few threads on alt.coffee by searching on silvia freeze drain. As for packaging, I prefer double-boxing and solid core foam instead of "peanuts". The loose foam shifts during transport and makes a terrible mess. A good pack-and-ship store will make custom boxes; it might cost $10-$15 in shipping materials, but it's assured the machine arrives in pristine condition.

I've heard that FedEx treats packages more gently, UPS' automated silo-sorting equipment is rough on heavy packages, and that USPS routinely drops boxes from a height of three feet or more onto concrete floors. Overall I've been lucky in the evaluation machines I've received, but several have shown clear evidence of a rough ride. Plan for the worse.