We had very nice tablemates....not anyone we stayed in contact with (but it was only a four night cruise). They had kids about our kids ages, made decent small talk. It was a first cruise for each of us, so talking about what we and the kids did each day, plus talking about WDW, got us through a lot of meals quite pleasantly. He was a dentist, my husband and I are functionally IT people, and we spent some time talking about technological advances in dentistry - which we found quite interesting.
(Remember, religion and politics are not polite topics for small talk)
Our next cruise will be the four of us, plus my parents. I'm not opposed to having others at the table, but if it does happen, I'm planning on making a special effort, since six against two (or four) can be overwhelming. However, my parents and husband can make interesting conversation and I think all the adults in are party are pretty aware of when someone is being "cut out" and when they want to be "left alone."