I received my voucher without any prompting. It gave a date as to when I would receive it and it arrived on time. I did have to wait about 3/4 weeks tho.
You do not say how long you have been waiting, but three to four weeks is the planned time, but often it can take up to six weeks depending on various factors. You will get your vouchers, I have received plenty myself, but you need to be patient. You can try emailing them using the link at the bottom of the FAQ page, but response times for replies is not great.
I sent off for a 10 pound Amazon voucher about a month ago & was gettting a bit concerned but Ive just been on vouchers on the "you" section & noticed that they are due to be posted on 5/9/08. Toluna has been behind with them but are now getting up to date. Good luck with yours.
I think you just need to be patient. I had to wait about 5 weeks for an amazon voucher (which does seem a bit ridiculous!). Whilst waiting, I sent a couple of emails about it and I got prompt and polite responses. You will get your voucher eventually!
If you go to your home page and look in the bottom right corner there is a news section and toluna have posted some infomation about the delays . Hope this helps.