Ranking high on nearly ANY word, including heavyweights like "sex" "dating" or even "viagra" isn't detrimental to website success. None of those words gives any substantial amount of traffic to sustain a business. You need "long tail" traffic to create sufficient volume. How to get links to your long-tail-search-destination pages? Links exchange and buying links is counterproductive. Building links to your long-tail content requires really interesting and unique see more content and nothing more. You'd sure need some link juice to jump-start deep-indexing, though, but not much.

Now, take a look at Google Instant, released yesterday. Matt Cutts commented that the new system induces even more long-tail searches and even less second-page clicks. What does it mean? It means that the "middle class" of rankings is now completely out of luck. If you rank 14th for "social network" - you're not going to get a single click a day! You would have to either rank #1-2-3 for "social" or look for luck at the "social network for fishermen in texas". Ranking for "social" is a problem - no amount of link building would get you there. Top 1000 search words would return massive sites that are impossible to kick out, because they have loads of "natural" links. For the longer phrase, however, you can't build links effectively, because you can't target specific anchors, since they are all too small and only work well in large volume. I think this is going to be a trend with search engines in the coming decade - links will mean less, content will mean more, natural links will help.

Pick your niche and become the best in it.