Tacit,
I have seen odd and unexpected beachballs in Safari since I upgraded to Lion, with as few as four pages open. One of the additional pages is often
www.msnbc.com, which may require more memory than most pages.
I have Safari configured to log in automatically at the MicroMat Forums at launch, and iCab configured to log in to the FineTunedMac Forums at launch. If I open additional pages in each browser, using bookmarks common to both, the responses of the browers are markedly different.
Now that you have posted your observations, I will check Activity Monitor and see if my experience is the same as yours, making use of the Disk Activity tab to check pageouts. There is definitely some new problem here.
