I also enjoy Southwest, not only for the ease of website booking but also if you have a change in plans, it is really easy to rebook or make changes to your ticket without incurring the regular penalty that almost every airline charges.
Southwest also now offers shuttle bookings directly from it`s website. That`s a plus if you are not renting a car, and prefer to book everything in advance.
Service will only improve with the older airlines when customers start asking for the improvements. Some other perks, not necessarily improvements I have noticed are ease in moving luggage to your hotel, directly from the airport (McCarren/Las Vegas, and I think Denver offers this service also).