I've just recently tried out Quibids and can tell you that they are legit, from the perspective that I received all of the items that I won.
The thing you have to watch out for is that it's easy to get caught-up in the excitement of penny auctions and as a result you can blow through bids very easily, which means that you could end-up spending a lot of money.
So here are my tips. Give the sites a try, you definitely can get some great savings. But start small. Either start off going after some less popular items or gift cards. Don't jump in just try to get an iPad for $20. I think you'll be disappointed if you go with that approach.
One other thing to keep in mind is that at Quibids, the money that you spend on an auction can be applied to the Buy It Now feature. Here's how it works. Let's say you bid on a $25 Home Depot gift card and did not win the auction. You placed 25 bids during the auction, which would have cost you $15. You could use the Buy It Now feature and only have to pay $10 for the $25 gift card. So these are the types of auctions that I recommend starting with. That way if you get caught-up in the excitement, you haven't wasted any money.
Good luck. You can try Quibids at http://qb.cm/r5489819