I bid on Ebay - a lot.
How many? I have 203 active bids. THAT much.
I only bid on Ebay because I did some math and financially speaking, when it comes to the newer stuff, your odds are better in simply purchasing the cards you need. Also, it's better off bidding on lots when you start a collection as it knocks out a significant number of cards almost immediately.
For example, the Goodwin Champions set that I'm building, I am 88% complete on the base set and 84% complete on the mini's. I'm around 40% complete on the relics and about 2% on the autos. My strategy is to finish the base, mini's and relics, the move onto the auto's.
I'm about the same with AG as well - only difference is I'm 100% on the base, but the various inserts make it a pain in my ass. So I've decided to focus on the mini's, of which I am only 34% complete, and the relics - about 30% there.
So when you see my list, you'll see what I need.