I originally was using VSD for quick mock ups but now have built some full blown sites using it too. The ability to easily add flash components and html code blocks means you can do some quite clever stuff if you need to.
The other really nice thing about VSD is that ANYONE can master it. My partner wanted to build a site for her book business but she knows NOTHING about html or where to start with standard web design tools, so I sat her on the computer, loaded up VSD and did the ftp set up for her. I gave her no help at all and she built
http://www.manorfarmbooks.co.uk - and didn't even use a template!
Then I started her using shopping cart/shopping cart designer and you can see she got on with those too. This is from someone who used to need help running a word processor!
She has since also picked up the coffee cup search program and I gave her some basic pointers but she figured out pulling it into VSD by herself.
If I was only allowed one web page building piece of software I'd make it VSD now, purely because you can put together a nice looking site so quickly using it.
Andy