I looked at it after seeing the adverts. I remember it works in a similar way to eBay. All goods start off priced at £1 then Madbid members bid against each other during the sale period. The highest bid then wins.
The thing I didn't like was that you can only bid up to an amount you already have in your Madbid account. It's not like eBay where you pay later or with PayPal - you have to put the money into your account first before you can bid! So, if a new TV sells for £250 that's because the winner already had at least that deposited in their account. If you don't win the auction your money isn't returned - it remains in your Madbid account and I don't think it's easy to get back. That means you are obliged to buy something from Madbid at sometime in order to spend it.
I didn't bother.