I applauded AT&T when they introduced the $15 data plan (for 200mb). The price was low enough that it helped my family go from 1 data plan to 4 data plans (out of 5 total lines).
In fact, that $15 plan has been one of the biggest reasons I've defended AT&T recently. Verizon and Sprint start their data plans at $30 last I checked, which quickly becomes prohibitively expensive for multiple lines on a family plan.
It's especially damning for AT&T because they refuse to allow any smartphones on their network without a data plan (even if you bring your own unsubsidized unlocked smartphone).
I realize $20 instead of $15 isn't a huge difference but it all adds up. Honestly, I was hoping they'd go in the opposite direction with a ~100mb plan for $10. Now that would've been a game changer.