My 3GS has just had to reload some of the tabs in Safari after I used the fast app switcher to reply to a text and then go back to Safari again. Up until 4.0, my 3GS has never had to reload any tabs in Safari, so the fast app switching must be taking a good chunk of RAM. The 512mb of RAM in the iPhone 4 should resolve this. The biggest issue is that even without multitasking and fast app switching, the iPad already has to reload Safari tabs. It seems to me that this can only get much worse when 4.0 comes out for the iPad, and that it really badly needs 512mb or more to operate properly without reloading content.