Right now there are over 656,000 expiring domains that you can pre-bid on at Namejet. Lots of opportunity there even if more people come. The key is to find those hidden gems and wait until 1 minute before they go off the board (assuming no one has bid on it yet) and then bid. This is the best way to attempt to be the only bidder on a domain and win it for $69.
Finally, you want to head over to domaintools.com. Then put the domain into here. What this will do is it’ll show you the history of the domain, because a lot of times these domains have been dropped like four or five times and a lot of people in SEO feel this way. I’m not sure about it. If a domain has been dropped several times, then Google does actually devalue the links pointing to that domain. So, as you can see I just changed registrars a few times and it hasn’t been dropped or else it’ll say one drops or two drops.
Here's a test I have in process.  I bought an old $5 closeout domain from Godaddy TDname expired auction.  I put a quick minisite up and linked to it with a crazy anchor text phrase.  The domain is ranking for that crazy term now.  It's gone through one pagerank update and I'm waiting for a second to come.  Then I'll redirect the domain to another minisite.  I suspect the second site won't rank for the anhor text, but we'll see.  
As far as flipping domains for a profit is concerned, there are certain domain names that are worth a lot of money. For instance, Hotel.com and Business.com have been reportedly sold for $11 million and $7 million respectively. Now even though coming across such golden domain names seems more like a long shot, you can still make a decent amount of money if you choose to buy and sell domains as a part-time business opportunity.
So how do you develop that instinct? NameBio maintains a database of over 500,000 historical domain sales (as of writing this post). They have interesting filtering features by which you can narrow down domains by price range, date sold, keywords and more. Simply sifting through the listings on NameBio long enough will quickly develop your domain appraisal “instinct”.