An interesting discussion going at one of the forums where a person claims to seeing different rankings when looking for the keyword websavvy when he changed the browser. Here is the explanation but this person

Switching browsers equates the same as another request to fetch a SERP from a Google data center. There are 100s of Google data centers and each time you connect to it, you don’t always get the same data center.

I always seem to connect to the same data centers in FF, and then a different data center in Opera.
And how do I know this? Because when I connect to Google in FF and search on just my site name: websavvy — it’s a normal listing (first position).

BUT, when I do a search at Google using Opera, I’m getting a different data center because it shows me a multiple URL listing for my site name: websavvy.

I did search for the same keyword and result were exactly what is said above. If its a fact then SERP has another mystery to unlock. I hope the SEO blogs like SEOBOOK, Search Engine Watch Blog, Daily Seo and others can take a look to see if it’s really something which is right.