hi rob,
a goto 12" dob is a great choice. I would recommend getting a flexitube model, as they are easier to move, as they are huge beasts!. if you go bigger than a 12" you will probably need a step to get to the eye piece.
you will get great views with that much aperture, great views of the planets and deep sky objects.
I have a skywatcher 12" goto dob. my photos can be seen here
http://www.flickr.com/photos/80336656@N07/
of course at the eyepiece things look not as colourful!
Cheers
Rusty