I'll start with what I know...
It is similar to Ebay, and yes, you bid on vacation components. It is different from Ebay in that you deal with Skyauction for payments and travel arrangements rather than with each individual seller (at least this has been our experience when bidding on resort accomodations). There are auctions for resorts, hotels, air travel, packages, cruises, etc.
To my knowledge, all winners are subject to a $15 fee per auction. Some auctions on resort stays are bid-per-night, which means if you win the auction, you pay what you bid plus a $32 per night minimum charge. These are seldom a good deal. Other auctions are for one week time periods at a particular resort. Some auctions allow for a choice of resorts with several choices of dates. These auctions for a week's stay have a minimum flat charge of $195...so you add that to the $15, and you pay $210 in addition to whatever your winning bid may be. You can find some great deals with these auctions.
There is also something called a Ready Set Go auction for week long resort stays. These run a couple of times a day and generally go for $50, give or take a few dollars. You can check availability in advance to see what resorts are available during the time you wish to travel. You can also contact Skyauction and reserve a resort if you see one you like prior to actually winning the auction. Great deals can be had with the RSG auctions...you pay the $15 plus $195 plus your winning RSG bid amount.
Orange Lake Country Club, Vistana Villages, and Cypress Pointe are probably the more desirable resorts in the Orlando area that come up frequently. If you do a search on the DIS regarding a particular resort, you should get some info to help you decide if you'd like to stay there and what a good rate would be.
I would definitely watch the auctions carefully for at least a few days before trying to bid.
Good Luck!!