I also only bid 3 to 5 stars. These sites idea of a 1 and 2 star can be scary. (And I routinely stay

Interesting story in the NYT about travel bidding sites , and how more airlines, hotels, etc, seem to be putting their unsold inventory on-line with them. Tips and tricks as well, for so-called "opaque" travel sites.
phoenix airport hotel I tend to stay in super-cheap hotels in a super-central location, so I've always thought that these bidding sites were not a good idea for me. I'd rather be in a good location phoenix airport hotel in a 1 star than in an inconvenient location in a 5 star hotel.
I use priceline phoenix airport hotel for expensive cities phoenix airport hotel like London. I routinely get 4-star business class hotels for around $80USD a night. The hotels are usually located in the Kenisington or Euston/St Pancras areas. For smaller cities like Amsterdam, it's not as good a deal as the hotels are usually located way outside the city center, and not accessible to public transportation.
We've bid a lot on hotels and have gotten great deals through Priceline. In the past few years we've bid a number of times in Seattle, also in Minneapolis phoenix airport hotel and San Francisco. We usually bid for the 4 star hotels and usually get them at 1/2 of the rate on the websites.
The caveat is you have to understand the process and restrictions, know the zone in the location where you're bidding, and understand it's non-refundable. I use the website biddingfortravel.com a lot to help with bid prices and the strategies they post.
I also only bid 3 to 5 stars. These sites idea of a 1 and 2 star can be scary. (And I routinely stay in those levels in Europe, but I have done my research before I book. There are wide varations at that level)
A few caveats. On Priceline you get a gurantee of ONE bed. PERIOD! And in Europe that tends to be very strictly enforced. There was a poster on the Marriott subboard on flyertalk.com a few years ago FURIOUS that the Courtyard in Paris charged his wife as much for the 'roll away' as he paid for the room. So if it's you and the kids going to Europe I would NOT recommend bidding unless phoenix airport hotel it's a site that lets you specify more then one bed. (Priceline doesn't!) This also holds true for major US cities, but folks seem to have more luck there with "pleading for exceptions"