andersry
The CABE architecture centres in the UK regularly hold public consultations and participatory events to engage the public in the design process of new developments. I work for part of this organisation. Sketchup has been used in this way. See document, might be useful. http://www.architecturecentre.net/docs/content/futurescape_report.pdf
and a whole load of links
http://www.google.co.uk/search?hl=en&rlz=1T4GGIE_enGB340GB340&q=cabe+architecture+centres+sketchup&meta=
Don't under estimate the SU learning curve though. Mr and Mrs Smith and their kids want to tell you in five minutes want they want in the new park or shopping centre, without training they can sketch it on paper a lot faster than they can in Sketchup. Sketchup is great if you have a week long consultation event, if it is just one day, get the pencils and paint out.
If you need more info pm me.
It is also worth mentioning that there is a general consensus that community consultations on urban design are often handled very ineffectively. All to often developers don't "consult" the public until they have planning permission and are about to start building. So the public's opinions at that late stage can have no effect on the outcome.
At the other extreme, empowering the public to draw their ideas, while important, needs to be handled very delicately. If not it can be disingenuous, as you can mislead them into thinking that they are the design team. They are the client, not the designers.
CABE have some good best practice info for public consultation.
http://www.cabe.org.uk/
