The actual unstepping is not really a problem. The mast just sits in the deck step and is not physically attached in any way, other than being supported by all the shrouds and stays. In fact, I've even considered cutting away the fore and aft sections of the step and inserting a pin from the side into the mast as a pivot point to make stepping/unstepping easier...but I digress.
Where I've encountered problems is at the base with the electric wires. TWICE now I've had marinas cut my wires short right at the base of the mast, rather than disconnecting them from my electric blocks down below. This has required me to do a really hard solder job just inside the mast base, oh, and a coax cable splice for the antenna!
Crane or self stepping/unstepping is the real question. As a background to the unsteppinng question, let me tell you about self stepping first: I've stepped a mast myself with just me and my wife (which I don't think I'd do again), but I reccommend at least one if not two extra helpers. I attached all the stays and shrouds (except for the fore stay) with the turnbuckles as loose as I could get them without actually disconnecting them which allowed the mast to go up without fear of toppling over. My wife pulled the mast up from the front while I guided the base into place/shouldered the mast up. I tied rope just above the base and anchored it to carabiners attached to the toe rail at the sides and rear to provide lateral support. Once the mast starts to go up, keep it going and it goes just fine...if you waver, well, cross your fingers...it's like trying to balance a baseball bat on top of your head.
I would assume unstepping would be the same, but I think it would be more difficult...it's kind of like felling a tree...a metal tree...although trees don't come with stays and shrouds attached, and they're heavier. But lowering is a more controlled affair and it gets 'heavier' as it gets lower and the angle of pull decreases...all while trying to gently set it down on the center of the deck (a mast never got bent or dented because it went UP too fast). I'd go crane for unstepping and self for stepping....unless you want to build an a-frame or similar old-school stepping structure.
Oh, see this link about another idea:
http://www.caphorn.com/sections/Pages/mast_stepping_system.htm