I just had the same bad experience as many others are complaining here.
After I was waiting for 5 days for my campaign to be approved and start running, and many emails to the admin to explain the delay, finally he said it was disapproved. I decided to ask for a withdrawal and get out there, so at the process according to their rules I should ask for a PIN which I did. Microworkers said that they sent a PIN but it's not truth. I never received in my email a PIN from them. I went to ask for the PIN to be re-sent but I noticed they say a $2.00 fee will be applied for every new PIN request. Then I realized this is their way to diminish the account money and not to send the requested withdrawal.
In domain search I found that this site is run by someone with the following information, but even when I tried to call him, the number was not working.
I would recommend to everyone with complaints for Microworkers, to contact their Credit Card or Moneybookers or AlertPay, fraud department, whichever is the way they paid and strongly complain against this scammer who runs this site.
Nhatvi Nguyen (firstname.lastname@example.org)
17311 Dallas Pkw
Dallas, TX 75248