I've enjoyed reading (some of) this thread.
I'll chime in with my experiences from 5
DCL cruises. We were seated alone for 2: 1 due to saling concierge on the Dream, and another due to my request (my hb is chronically late, and I did not want to hold up the table). Remaining 3, my son and I were seated at 8-tops. First was with a single dad with his daughter - a little awkward for a few minutes, but ultimately really fine, as the kids hit it off. Never met the other family, as they never showed for dinner for the entire 5-night cruise.
Remaining 2: I was SHOCKED by how well we all got along! DS and I seated again at 8-top, this time with 2 other couples, each with 9 yr-old, 3rd grade, only-child boys! The boys were best buddies by the time appetizers were delivered for the very first dinner, and the adults (2 couples and myself) hit it off so well that we went to Palo brunch together, spent much time together between meals, etc. They even invited us to visit them this summer, which we did, and enjoyed tremendously.
Last cruise, DCL worked their magic again: my DS9, his BFF(12) and I were seated at an 8-top with a lovely couple and their very well-behaved sons (ages 12, 10, and 6). The boys sat across from each other, I sat next to the mom, and the dad and 6 year old were on the opposite side. Dinners were terrific, with the boys having enthusiastic discussions about Legos, Star Wars, etc., and the adults having their own great conversations.
Moral for me: I look forward to meeting our table mates. DCL really seems to know how to work it out, and I've come to trust the process. If it ever doesn't work, there are numerous alternatives, so I don't sweat it.