Good question, jackal, and unfortunately I don’t really have a definitive answer. Overall I like the “fun” Southwest attitude. Southwest has gone from being the ultimate low cost carrier to our country’s “premium” airline thanks to their lack of fees and upbeat attitude (not to mention profitability), which is great. I think that attitude works well in the markets they serve, since most of their passengers are American, and largely not frequent flyers. I think even the frequent flyers don’t have a problem with the jokes, because the whole Southwest experience is so upbeat and positive. Even if they don’t like the two minutes of jokes, they’ll love the great service, on-time flights, and efficiency. A positive attitude rubs off on everyone, and as a result I think you’ll see a lot less complaints from passengers on Southwest than any other US airline. In a way I'm jealous.
At the same time, I’m not convinced that “attitude” would work in an international market where you’re dealing with passengers of various nationalities and cultures, at least the jokes. Great customer service works in all markets, however. 😉 What may seem funny to an American might not be viewed as a joke by some foreigners, who may very well take offense.
At the end of the day my favorite type of service is the professional yet friendly attitude that many premium foreign airlines offer. That might be tough to do in the US, because keeping a workforce motivated while being serious can be tough (especially with unions like the AFA). I guess ideally there would be a compromise, with a “fun” attitude, minus the plethora of cheesy jokes to appease the frequent flyers. I actually find lots of those jokes funny, though (as surprising as it may be).