I've been reluctant to use anything but Excel for a long time... the last vestige of being a Windows user, I suppose (even though I haven't been one for over 1.5 years.)
This thread got me thinking though... I recently began using Pages for all of my assignments (college

it looks better on my monitor and isn't crapped up with all kinds of menus and toolbars and whatnot (Inspector rules!) I use Keynote for class presentations (even though they have to be converted to PPT so I can use them on my professors' computers, and it ruins the beauty of it all.)
I created a spreadsheet in Excel about a year ago; I was spending way too much of my loans too soon and not realizing it, which caused some horrible money problems. Tonight, I opened up Pages, created a table, and got it all set up. It looks much nicer than Excel, and was so much easier to use (especially my equations; very easy to set up.) Plus, my iMac has the stock 512MB of RAM; Rosetta is impressive and all, but my computer takes some time to open PPC apps, and sometimes takes too long to modify things once opened.
I suppose it probably depends on your needs; if you've got to swap files with other people all the time, or have some heavy-duty uses, Excel or OpenOffice/NeoOffice would probably be better. If it's for personal things, I'd just use Pages. Truly great (and I was a real Pages skeptic up until about 6 weeks ago.)