Price really. I only receive the emails for AA's Netsaavers and the CO equivalent. AA's are priced as one way fares and never look appealing whereas with CO the price shown is roundtrip with options to burn some miles + cash if you want instead. Their roundtrips price at a significant discount whereas AA usually just looks worthless to me. Recently I saw LGA-ORD pop up on my homepage for something like $72 each way which isn't bad, but I'd have to come back on a Monday morning which isn't something I can easily convince my husband to do.

The NetSaavers never really strike me as "WOW THIS IS A BARGAIN" types of fares. They usually price out to something that I would've probably paid anyways if I actually had to fly that route and planned it 4 - 6 weeks in advance like I usually do. Now if they were actually "WOW THIS IS A BARGAIN" fares and especially for some international routes, then maybe I'd start to get excited.