I earn about 30-40 a month on my amex, but I buy alot of groceries and pay for bills with it so it pays for itself and then some.
I just got the Uber card a couple months a go but I took it on a couple trips with me and earned around 100 bucks so far(That's not counting the 150 bonus they gave me for spending 1500 or so within. 90 days) But when I go out of town I tend to eat out alot any way, might as well make a lil cash from it.
The cards with the rotating categories are hard to pen down, last month I made 75 off of discover because it was 5% cb on PayPal purchases, and I just happened to be getting house work done, guy billed me through pay pal so I payed with the discover and then just payed discover off.but other months I rarely use it other than to pay off a bill or something.
I'm only using the cards for stuff I would already be spending money on. And I don't carry a balance so I never pay interest.
I think it's worth it if you can find a card that suits your life style (preferably with out an annual fee).
Check our Reddit
https://www.reddit.com/r/churning
As you'll see, it's a whole life style dedicated to getting bonuses points cash back etc.
Also nerdwalle.com is a good way to compare cards.