The introduction of the iPad has made our lives as FAs much easier with respect to drink payment as they are much more reliable than the old handheld devices, and all receipts are available online. If you have tools that work, employees will use them more often. We have not been told by management to reduce how much we comp drinks - we are still encouraged and allowed to provide free beverages in the event of a special occasion or service failure/delay/etc. Personally, I am more than happy to comp when it is appropriate and builds goodwill; at the same time it is frustrating to be given an incredulous look when asking for payment for a beverage during an on-time flight that has had no service issues or delays.
(As always, the views expressed here are my own and do not necessarily reflect those of Southwest Airlines.)