I have been doing lots of keywords research and that has almost always paid me handsomely. I have plenty of articles hitting the top Google spots consistently (but can't give more details as they are owned by another site now).
One thing I must mention here is that the age of that site and its popularity has its influence on the success in Google rankings too. Most of the very competitive keywords / keyphrases have stayed at the top against millions of competing web pages even after 10 months or more now. But some have fallen below others now because people are working on these keywords and my site isn't updating those pages with fresh content... Something that's not in my hands because I don't own the site.
But this proves that there are many factors that influence the success/failure of your strategies. Competitive keyphrases are just that -- Competitive. If you beat other, then there are going to be others who will beat you... in this case, you have millions of web pages who have smarter people constantly working at it.
Now, if you are using top articles submission sites like the EzineArticles, you can achieve the same good results with competitive keyphrases and millions of other competing web pages.
Little competition:
Put your keyphrase in surrounding quotes and check in Google. If there are too few results and no Adsense ads on the 1st result page, then that keyphrase is ignored by everyone concerned. It could also mean that this low-competition is a possible gold mine waiting to be tapped. To know exactly which of the 2 you need to check the keyphrase in various ways to see if the surfers are using it but the marketers are either unaware that there is a huge market out there, or simply are not capitalizing on it.
Another point, what is not clicking today can be a hot property tomorrow, so you need "Vision": For example, "barrogz" is relatively unknown today (or is it?! I can see approx 6,000 results in Google for this keyword!) -- but it could be a hot property like the keyword "Bill Gates" is for so many decades now!
So, there are many parameters attached to a keyword research / SEO. It's is like a game of chess and you need to analyze many different variations to come up with a great success strategy -- applicable for both short-time as well as long-time success -- like in Chess, the strategy is constantly worked on to keep moving in a favorable position and also to beat opposition. It applies to SEO too.
I think, to achieve success in SEO, you need to be very analytical in nature, extremely focused, and possess a good knowledge about the field and about what you're trying to achieve in it.
