This is what you see if you go to community.secondlife.com, a message of unintentional irony. Linden Lab's official Second Life community portal was announced to launch February 28, but company spokesman Peter Gray points me to the official status delay:
As many of you have noticed, the Community migration is taking a bit longer than planned. As you might imagine there’s a lot of complexity in the structure; and because we strive to preserve all of the KB, Blogs, Forums, Answers etc as they were, we’re being extra careful in verifying everything is in order. Linden Lab is actively engaged with the new provider to get the new site up and running as soon as possible
SL Universe, the longest-running unofficial online forum for SLers, is probably your best bet in the meantime (and in addition after that). Second Life Friends on Facebook is pretty good, as is this Reddit group, though both run heavy on SL fashion advertisements, if you're not into that sort of thing. In comparison, SL Universe has some of the richest content and most expert opinions (if also the heaviest snark). Plurk is great, yes, but the user interface separates individuals conversations on a timeline, generally making Plurk difficult to use as a "community" in the typical sense.
And, of course, there's always any appropriate comment thread in this blog for community!