Personally I have stopped counting at 1,000 social networks, but it seems that the latest trend is in growing your home-variety of a social network. After Ning we have seen several other vendors cropping up, offering free of charge white label social networks to experiment with, but none have become quite as popular as Ning so far. However, this doesn't mean that vendors should stop trying :-). The new kid on the block is called Neeetz. The design is simple, straight forward and clean, nothing fancy. Although I haven't created my own network on Neeetz (just a profile to get a feel for the product), it seems as easy as Ning.
The 1 million dollar question remains then: why would the market start prefering Neeetz to Ning, Ning having gained a large crowd of followers already? This remains to be seen. As Neeetz has only been active for two months, it is too early to tell. One feature I liked (and can't seem to remeber having found on Ning) is that you can choose to select networks from specific countries. This saves you time if you're only interested in local contacts.
We'll keep an eye out for them and see what new features are available in the next six months.
Tip for the Neeetz team: check out the Q&A at Ning; it will let you know what users are looking for instantly without any marketing research ;-) !