I have family and friends who have individually acquired many, many millions of miles/points courtesy of the US card spending-related earnings on just their usual spending activities. It's rather sweet for me too, but some of the European airlines tend to make more award space available to their own program members than to the partner airlines' program members, so for us heavy North/Central/South American program users, things aren't as sweet as they used to be.

Personally, I'm more interested in earning hotel points than I am in earning airline miles/points. There are enough airfare deals and tricks out there that earning miles from flying for use to fly just isn't of as much interest to me as it used to be. When I'm getting US-Europe, South-America-US/Europe, and Europe-Asia roundtrips each way in business class flatbeds for $650-$1400 -- even during my peak vacation times -- earning miles from flying and non-airline partner activity just isn't as material to my travel plans as it used to be; and in large part this is because long-haul premium cabin award availability is not what it used to be.