I guess I'm in the minority, I am an advocate of the younger trend. I think most of the opposition coming from those in school and those applying now simply comes from envy - mad that this trend was not as "hot" while they were applying or when they were still in school/younger or they are upset that 2+2 programs didn't exist for them - and those who fear for their chances of admission over the next couple of years as these 2+2er's enter into each respective school, making fewer spot available. I have known that I wanted a MBA since my junior year in HS, and I too wish there was a 2+2 program when I was a senior, I feel I actually had a stronger profile then and would've had a better shot at H than now.
Secondly, I think a lot of people are overlooking the management/leadership experience younger people, especially the type to be accepted into a 2+2 program, have gained by leading clubs, student government, teaching courses at school, community involvement etc. Even at the typical 3-6 years experience, many (not all) of us aren't managing or leading people on any substantially different scale than we did in undergrad.
As far as the classroom, let's be honest, aside from those of us really looking for a certain set of technical skills, business school is mostly about the network and job options, not the business education - finance and derivatives is the same at No Name Community College as it will be at Wharton, the only difference is the brand. It's great to hear someone else's perspective on a business problem, but after 2 years of working, you've experienced or heard about enough business problems and seen/implemented enough solutions for you to be able to contribute your obligatory 1-2 comments per class.
Lastly, I think it's time that business schools recognize that people have clear goals for themselves and would like to attend b-school at a younger age. Every other graduate school program (ok, maybe not some selective RED programs) allows students to come straight from undergrad. Why should someone have to postpone the next step in their education just to get into school? And as a woman, I'm really sympathetic to this as business school and trying to re-launch your career post-graduation and establish yourself as a professional cuts into your prime childbearing years (for those of us who want kids), postponing the whole ordeal affects your personal and professional life. Who cares if compensation takes a hit, 25/26 y/o graduates coming out making 80-90k will be doing a whole lot better than the majority of their peer group who are still in entry level and/or very junior roles. And of course, a lot of employers find it easier to hire younger students into these "level 2", long hour, analyst/associate roles.
The only downside of admitting the 2+2er's is dictating what will be appropriate experience in those two years before they come. If you already know as a senior that you're headed to HBS, what makes you obligated to take crappy 9-5 or 60-90hr work weeks in MC/IBD?
Overall, I think the longevity of work experience is overstated and it's definitely more about the quality, especially coupled with outside experiences that present just as many leadership and problem solving opportunities. I applaud the schools who recognize this and am happy to see focused 23-25 y/o's being more openly welcome into top b-schools.