The result in position 4 has been rotating between three different firms all day for our industry's top value keyphrase. All other listings above and below remain constant.
It happens all the time for couple of reason 1. You may be hitting the different data center 2. Google is updating (Which is normally very often.)
shabbirbhimani is right.. or it could be due to google dance or just a simple tweak because of the updates. Try this tool so you could see and compare your SERP to different data centers. http://www.mcdar.net/dance/index.php
Persanalised search - Google might be taking into account your IP and browser delivering new results every time...
The results below are still the same? heh this is interesting - also what do you mean by 3 different firms?
You may be logedin in your Google account.. and another thing try to search after deleting your cookies.
SERPS change alternate all time .... that's why so hard to gain a top position and stay there... olso if it's about new sites google dance adds up olso ...