When end users finally decide to buy their brand it usually a quick process (google search, directly to website address, largest domain marketplaces gd sedo... not many at all would ever wait for their desired domain to go to auction someday.
But some very large multinational companies have been known to use auctions frequently. There's always businesses looking to expand and keep updated on auction listings. Some patient end users might also be waiting for their perfect domain to finally come to auction....
Can't beat namejet and godaddy at the moment for auctions. That's where the traffic and bids are.