For once Microsoft actually came up with a useful update in their Office short of a fancy new colour scheme - the new Ribbon thing. I tried the MS Office 2007 beta and found it really intuitive, but wouldn't pay the ridiculous amounts of money they charge for it. I think they even decided not to patent it so that others can use the idea. Now I'm no fan of Microsoft (although we've been pushed into a Microsoft world) but the day i see this in OpenOffice is the day I rush to download it.
But I think extensions is a great way to go - it's the most powerful feature in Firefox and is mainly the reason I miss it when I can't use it (god bless Adblock).
For now I plod along with Web-Based Office apps (namely Google Docs) till the day desktop based ones become worth their Hard Drive footprint, or I need all the features they tout.