I've been watching Firefox 3's ram usage on my vista machine, and this is my set-up:
QUOTE (My Main Profile)
Addons:
Adblock Filterset.G Updater, Adblock Plus, Addictive Typing Lessons, Ctrl-Tab, Download Statusbar, Feed Sidebar, Fire.fm, FireGestures, Flashblock, GooglePreview, Locationbar2, Menu Editor, Microsoft .NET Framework Assistant, MR Tech Toolkit, Open IT Online, QuickJava, Stealther, Stylish, Tempomail, Thumbnail Expander, United States English Dictionary, Yet Another Smooth Scrolling.
Theme:
HEAVEN.CUBE (usually), Proto(v1.1.1pre2) (not so much anymore).
With 8 tabs open, and the Feed sidebar checking 18 rss feeds, I only use 67MB of memory.
QUOTE (My low-weight Profile)
Addons:
Adblock Filterset.G Updater, Adblock Plus, Firebug, Firecookie, FirePHP, Fission, Flashblock, Menu Editor, Microsoft .NET Framework Assistant, QuickJava, Zotero.
Theme:
Chromifox(occasionally), Littlefox (mostly).
With 8 tabs open, and everything opened up, I only use 45MB of memory.
QUOTE (My gf)
Addons:
Adblock Filterset.G Updater, Adblock Plus, Color Management, ColorfulTabs, CuteMenus - Crystal SVG, Fast Dial, Flashblock, Forecastfox, Glasser, GooglePreview, Microsoft .NET Framework Assistant, oldbar, QuickJava, Stylish, Thumbnail Expander, Yet Another Smooth Scrolling.
Theme:
XP on Vista
With 8 tabs open, it only uses 46MB.
Although, I might be a little more yahoo about Opera, if I liked it.
Chrome is a new refreshment, though, from the general browser war material.