As you say, United sucks for many, many reasons, but this is a step in the right direction. They're realizing that carry-on bags are the biggest single reason for delays, exasperated flight crews and grumpy passengers. Perhaps they finally woke up and said "wow, Southwest is really kicking our ass...I wonder why?"
As for flying United, I avoid them whenever possible flying domestically. The Company, however, views them as preferred. However, they stopped flying to Bangkok, instead giving all their business to their "partner" ANA. Since it's damn near impossible to get a flight that runs through Tokyo on ANA without like 9 years advance, I'll be flying Qatar Airways to Bangkok at the end of the month. Apart from going the other direction, there appear to be multiple perks. First, everyone I know says Qatar is hands down top three in terms of service. Secondly, their business class lounge in Doha is fucking ridiculously sweet, and since I have 9 hours to kill there each way (because I'll be going the wrong way), I plan to take full advantage. Finally, their *business class* seats are the same as United's *first class*. So I'll get more room for my XXL ass (not that there wasn't enough on United, mind you, just the more room the better). If all goes well, Qatar will be my preferred airline to Bangkok and Kuwait.