Hi all
Moz and Melissa are right on the money. I can't see any downside to doing professional work pro-bono for a not for profit, other than potentially reducing job serach time. Unless of course the not for profit is the "Australian Nazi Party Whale Hunting and Kitten Strangling Club"

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The potential benefits regards showing willing and desire, keeping skills current and making contacts are great. It's all about how you sell teh actual skills and competencies used in the role, and teh achievements delivered, not how much they were pauid for it.
If I was reviewing the CV's of two applicants, both recently redundant but one who sat at home and one who set out to do volunteer work, I know which one I would look more favourably on!
Thoroughly recommend contracting work also - especially if they are doing nothing otherwise (as long as they are able to end the contract in a reasonable timeframe to take up a permanent position that may arise elsewhere - check the exit clause). It worked for me - a three month contract was rolled over and over until it had stretched out for a year, when I didn't seek another rollover as I had been offered a permanent job elsewhere, the company I was with counter offered. Eventually I returned on a permanent basis a few years later having left a good impression and maintained the relationships.