I actually tried to use iPods to drive traffic to a site of mine a couple years ago. It didn't work very well but I think the reason was that I didn't make them do enough to get the prize. Just make sure that 5 new reviews on your site is going to create enough value for you to warrant the cost of the iPod.

Without knowing anything about your business I would suggest that you look at some of the Minimum Viable Product ideas for customer development. Smart use of Google ads could go a lot further than an iPod giveaway.

just my two cents.