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I usually use Firefox and Camino. Both on a Mac. Rarely I turn to MSIE for Mac, and I have been experiencing the same thing. The worst case was a few weeks ago, when Firefox showed one of my sites as #1 and nobody else could see it.
However. Trying some keywords right now I can't repeat it, except for the disturbing fact that Google shows different results on google.com and google.[insert any European TLD].
Do nslookup google.com
You will see 3 or more (or less) IPs returned and your SERPs is delivered by either of them. If they contains differents SERPs, you will see different SERPs. SERPs are slightly different between datacenters.
So you can keep refresh on the same page in IE and you can see different result just like you see in different browser.