I'm all for it but agree with the points above. Target the long term scroungers first. It would also be beneficial if the work being performed could be something the person learns a trade in - repairing a road for example.
On a similar note I was on a bus the other day and sat behind two charvers. Their conversation was along the lines of how they had been sentenced to 500 (yes 500) community service hours (must have been a serious crime) and they were boasting how they only did 80 hours.
The foreman (or whoever 'looks' after them) told them not to bother coming back.
If this 'help in the community' scheme is to work they better find a way of monitoring it.