After an entire day of performance tweaking, I can finally report my results on FF3.
On the bright side, the Mozilla team has certainly made progress with FF3. Memory usage is not exactly lower, but rather more efficient. In other words, unused memory is quickly returned back to the OS, while FF2 would still 'hold it' for longer, causing the leak. However, the actual usage of memory per page opened is still high, but not prohibitively so. To be fair, with the exception of probably Dillo and Lynx, all decent graphical web browsers do utilize a considerable amount of physical memory. The other main advantage of FF is obviously the plethora of plugins, themes and add-ons available, something any other browser, including IE lacks.
On the "need to be improved" section, I will comment with comparison to Opera, which I consider to be closest competitior to FF. With speed tweaks, the loading time is nearly the same on both browsers. However, Opera wins because its more responsive as a software program. For this test, I tried opening a variety of sites, including Java script heavy ones and those that have poorly written HTML. FF can still be made to 'hang' when trying to render a page. By 'hang', I mean that it stops responding to mouse clicks and I can't even CTRL + TAB to switch to another tab. This is a problem that Opera, and even K-Meleon do not suffer from. Even when unable to render a page, the software program should ideally remain responsive to external commands. This one problem results in FF having an overall sluggish feel on windows. Surprisingly, I do not suffer this problem with FF on Linux, but I did not have any extensions installed on that machine, so perhaps its not the best comparison.
Hence, at the end, my conclusion for now remains the same as it was with FF2 and Opera 9.2 : FF is a slow moving ocean liner packed with hundreds of features and an onboard swimming pool while Opera is a speedy boat with minimum features that can possibly satisfy mainstream users, but not more. Now, if Opera went open source or made it easier to write third party plugins, they can steal more of FF's thunder. But, that seems unlikely at present since Opera is a profit oriented company while Mozilla is a non-profit entity.
And IE is probably the Titanic...