The true benefit of the government's workfare plans- making the longterm unemployed to unpaid "community" work, is getting people back into the habit of work. As such it is probably going to be beneficial to most of the supposed victims in the long term.
The two concerns that I have is the amount of time being talked about for the work- 30 hours a week for 4 weeks is quite a lot when they are also supposed to be looking for work. I realise it is less than a typical full time work week but I think it is too long for people unused to working regular hours.
The second concern is that the work shouldn't be demeaning, getting a qualified engineer to spend all day is a bright yellow jacket picking litter is not going to restore his morale.
It is probably most beneficial to people who have never really worked rather than those who have lost their jobs.