Would you care to expand on your experiences with this? I keep hearing of people who take this approach, but I've always been skeptical on how well it really works out.
Assume that I have a job. What you would be offering me would be an opportunity to quit my job in return for a temporary job that might or might not convert to full time. During the transition, I will lose my benefits. Your assumption of a pay bump when going permanent also seems to indicate that I wouldn't be compensated for the risk of a permanent position not being offered.
What do you see as the value proposition for an already-employed person in this arrangement?