Hotel booking sites often offer a "mystery hotel" at seriously cut-down rates, but the risk you take is you don't know exactly which hotel you'll get (and whether that means extra expenses). But with a little search sleuthing, you can book a mystery hotel and be confident you know which one it is.
Blokey blog Everything For The Man details a process that can help you narrow down the mystery hotels offered on Wotif.com and LastMinute.com. The strategy is pretty obvious when you think about it -- get the hotel booking details on screen and then conduct a search in a second tab for a hotel listed on the same site that matches those criteria. By methodically working through each option (star rating, reception, Internet and so forth), chances are you'll be able to narrow down your "mystery" hotel to the only one that matches.
Obviously, this won't always work, but as EFTM notes, it managed to successfully predict Hong Kong hotel rooms using this method, which is no mean feat in such a crowded city. Hit the post for full details, and if you've had a good or bad mystery hotel experience, tell us in the comments.