There have been threads about DBT recently on here. You could look them up if you want; I'm not good at figuring out how to post links to threads.
I am in my second cycle of DBT. Each cycle is about 6 months, and my group meets weekly for 1 1/2 hours. It's quite structured, not really like group therapy. You don't interact very much with the others in the group though I've become close to a couple of them. In my group, and probably in others, people keep coming in and out. No one necessarily starts at the same time.
We follow a manual based on Marsha Linehan's book on DBT. She's the founder of DBT. We have homework, as well as the diary cards, and we share them in the group. We learn the core skills, which are basically mindfulness training, and then learn distress tolerance, interpersonal effectiveness, and emotion regulation skills.
The diary card isn't hard. There's not much room to write, so you can be brief. You describe a trigger situation, your feelings and intensity, your urge, the DBT skills you used, if you did, what you did, and your distress level before and after.
It's not like therapy, though some of us shared personal stuff more than others. My group wasn't stressful at all.
I also liked that in the beginning of each week, we did a different mindfulness exercise, as instructed by the DBT leader.
I think DBT has been very helpful for me though it takes time to remember to use the skills, and what they are, at the time I need them.