Threadwatch links to a blog post named Google SERPs Platform Dependant? that shows how a search for a query on Google, on the same network but on two computer operating systems, can product a different result set. The screen captures documented show the differences between a Mac and a PC.
I personally ran the test and I found slightly different results for the keyword phrase "sports" on a Windows PC versus a Mac. Is this out of the ordinary, I do not think so. I have found that Google changes the results sets based on the following criteria;
(1) Geographic location
(2) Personalization preferences
(3) Data center accessing
(5) Operating System
(6) and some other methods.