A really helpful Search Engine Watch Forums member wrote an extensive post on a case study for long tail searches. The user found an interesting result:
In otherwords, only 31% of our traffic comes from the main search terms, while 69% comes from the long tail.
Additionally, search engines aren't everything. There are other ways to get traffic:
Search engines are not everything. All together, we only got 224,325 visitors off of search engines. That is less than 1% of our total traffic. Most of our traffic comes from other places. Anyone putting all the hopes on search is missing 99% of the traffic that they could be building. The rest comes from other marketing efforts, quotes in published works such as books, software, magazines, as well as news casts, word of mouth, inbound links, billboards, commercials, etc.
So how do you optimize for long tail searches? Write. Write a lot. Keep your site content-rich (and readable to the user). Target terms that your users may search with.
For more long tail analysis, Chris Anderson has written a book on the Long Tail.
Forum discussion continues at Search Engine Watch Forums.