There are many reason why you may not see the result.
* The page result may vary from different countries.
* Google even see the Browsers to show some results. [ http://www.youtube.com/watch?v=tNvswKFY17E ]
* Some time it happens for the people to click on 6 or 7th result because of the Title keyword and description that are catchy.
* Moreover, google page result changes often. If your site is found crapy or high rank domains are available, then your page result should be turned down.
* Your search history can also change the page results.
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I do check ranking often in this site :
http://www.seocentro.com/tools/search-engines/keyword-position.html
Some of the reason why I use this site is,
*Only for the First time I have to type captcha code and check many result.
*Show related searches.