I love the rough sketchy look when it comes to idea sketches, GUI wireframes and paper prototypes.
This is much more fun than this more rigid way of presenting wireframes:
Despite being visually pleasing, I also believe the sketchyness seen in the first image serves another purpose:
Keeping yourself in *ideas mode*
That is, whilst sketching and discussing, the limitations of the tool reminds us that we're not trying to reach perfection.
It reminds us that we're exploring. The tool won't let us be perfectionists, so we have to focus on different things. The tool channels us into thinking at a different level of abstraction.
What about software support?
Unfortunately most prototyping/wireframe software doesn't seem to embrace the sketchy look.
In fact, I've only seen one that does it natively. It's called Balsamiq Mockups.
Someone also has produced a cool stencil for Omni Grapple (Visio like tool for Mac OSX). These produce quite a cool result:
What do you think?
Personally I enjoy seeing wireframes like this. They communicate that the diagram is rough, both during and after their production.