There is an outstanding subscriber (paid access required) WebmasterWorld thread that discusses the topic of short term versus long term phrases. These are the types of threads that make me feel, hey - that $150 subscription pays for itself. Without giving up all the details, let me explain the premise of the thread.
We all know that searchers are getting smarter at searching. Searchers are now much less likely to search for [cars] when looking to lease or buy a new car. Searchers are now much more likely to search for a more specific search, such as [lexus es 350]. The same applies to electronics, instead of [digital cameras], searchers are now being more specific with [canon powershot camera] and so on. Searchers are searching less often on the short phrases, such as one or two work keywords and more often on longer phrases (long tail), such as three, four or five word keywords. The WebmasterWorld thread gives examples of this happening via Google Trends, log files and experience.
If you agree that searchers are searching less often on short tail keywords, then you might agree that SEO, today, is less about those short tail keywords and more about the longer tail keywords.
The thread discusses how many SEOs are noticing less traffic on those short term keyword phrases, then they have in the past. The debate then gets into the niche or industry of your keywords. For some industries where the searcher is less experienced, the short tail keywords still are very high. But for other industries, those short term keywords are experiencing less and less searches. Yes, this has an impact for SEOs and how they optimize sites.
Forum discussion at WebmasterWorld (paid access required).