I don't have a problem with it, if you're not in an exit or bulkhead row.
Those are generally considered, particularly by business travelers, to be the best seats on the plane. Part of what we earn by giving southwest thousands and thousands of dollars of business, is first crack at the good seats, and overhead bins.
So when a guy gets on, who was not in business select but was high on the boarding list, so probably an a-list pax, grabs the only 2 seats on the plane that have no passengers on either side, while his wife clearly wandered onto the plane 20 minutes later and was enjoying a beer instead of waiting in line, it was irritating.
It was flagrant, and his attitude about it was equally annoying.
As far as I'm concerned, you can save 3 entire rows in the back of the plane-- I don't care. But when you grab the BEST seats, and take one for someone who does not have the right to it (since they're boarding 80 people behind you) it is an obnoxious thing to do.
It would be exactly the same thing to me as having one person wait in line, then calling a family of 4 up to join you at the last second. Is it against the rules? maybe not. Is it really rude and obnoxious? Yes.
Wait one here. What I hear you saying is you don't care where they save seats as long as it isn't a seat you want. I find that annoying and an obnoxious "entitlement" attitude. Anyone can purchase a business select fare and get that wonderful boarding number and get all those "perqs". You don't know what that couple paid for the fare and the fact that they had a lower boarding number entitles them to select any seat they want. The factors in the woman's boarding later than you would have liked means really nothing. All it means is she was doing something that may have caused her to be delayed in boarding, it really does not matter what she was doing. Saving seats is not against the rules, deal with it.