I've gone to a couple GrubWithUs dinners, and they were great. I met interesting people, had interesting conversations, and even made some new acquaintances.
I didn't "make friends," though. That's a much different thing, and comes from a different place. The original NY Times article made great points about our changing nature as we mature getting in the way of deep friendships. That's all true, but there are also logistical practicalities.
The great friends you make in school or college are people that you saw every day, or at least every week, in class and around campus. You shared groups and activities, whether it was a sport, a band, drama club, your D&D group, whatever. Friendship takes repeated exposure in mundane situations.
I've had some great, intense experiences with acquaintances as an adult. A few years ago, I took a cross-country road trip with a guy that I met through a mutual friend. I was writing an article about the Smart Car, and he was my photographer. We drove 4,000 miles over 12 days, and had a great time. We both live in New York, and I even run into him at the occasional show. Without a regular, everyday reason to hang out, though, we just faded into acquaintances.
For people who want to have real friendships as adults, maybe what we need is some kind of structure in our lives that more closely resembles what people have earlier in life. For myself, I still have a D&D group, and while I don't want to hang out with everyone all the time, I have made some real and lasting friendships in the group. I'm sure most people could think of some way to find structure and camaraderie on a regular basis. I don't think GrubWithUs really does that, though.