I would suspect that you would want to pay attention to where your users are. If you're a Web 2.0 social network site, then Twitter is probably essential since

I would suspect that you would want to pay attention to where your users are. If you're a Web 2.0 social network site, then Twitter is probably essential since most of your users would likely be using Twitter as well. Same things goes for Delicious. If you're in the US, then look into getting a presence on Facebook or MySpace (MySpace especially if you're working with music). If you're somewhere overseas, then Orkut may be worth a look. If you're a design firm, it probably wouldn't hurt to have a Flickr account. The answer to this question seems to depend on where your users hang out. If they hang out on the web, then be on the web. If they hang out at trade shows, then go to trade shows. (Sam_in_nyc, I read your profile so know that not all of this applies directly to your situation, but maybe it's useful for thinking about the more general case...?)