yes, many long rich-keyword names are good different and specific things, but for a social network is a no no no for long names. IMO. ~Mike
Short name is desirable but most probably never available. Then we have to choose the one among the available one - sweet, easy to remember and including your key words. that would be best.
Domain names can be of any length up to 67 characters. You don't have to settle for an obscure domain name like avab.com when what you mean is AcmeVideosAndBooks.com.
I think 2 or 3 keywords inside your domain are more then enough. Because a long name won't appear that fast if you're out of for SEO.
Short name is easier to memorize. But keep in mind, the name should reflect what your team stands for. if the name you are looking for is not available, try abbreviations.
For these types of site where you want to make users aware of your brand you always have to get yourself a somewhat medium to short sized domain name and try to make it catchy. That's not a necessity for the catchy part but just look at twitter for example, the name is short, rememberable and catchy. Now whenever someone talks about twitter you now it's that website with the blue bird logo (or whatever it is). Try as best as you can to make something similar to this. EDIT: And by the way your first post in this thread is spot on about what should be done. That's exactly the idea to follow.
Shorter the better. Avoid long domain names. Also use relevant keywords in your domain so it relates to the niche you are choosing.
I don't know about it more because i don't having any website but i can say you something website name could be short or long it doesn't matters.Matters the website name which would be very effective that having some meaning.