If you haven't seen it yet...
http://www.google.com/googlespreadsheets/tour1.html
Meh, just look the spreadsheet version of http://www.writely.com/ (which they took over) and I'm not finding that useful in the least bit. Though I guess it's because I have MS Office.
Personally, I feel there are some things that should be left for local installs :)
I haven't checked it out that thoroughly, but it's cool to think you could keep files and work online from anywhere. I think that's the appeal -- at least to me, that I wouldn't have to buy anything and I could work from literally any pc with a browser. For non-technical people, it really simplifies things :) Plus, I imagine it would be OS/platform independent as long as your browser could parse whatever language it's written in.
Yeah I guess you're right. I guess I don't see the point personally because I have Office on my laptop, and I don't really use any other computers when I travel. That, and I hardly ever use Word or Excel so yeah :P