(I don't like the fact that you have to register for googledoc as that just seems a way for them to include your email in their mailing lists and send more spam mail crap, so I'm concentrating on Open Office)
I would say the main benefit is that you don't have to worry about which version to install on which computer, as its all the same. For instance Mac users, such as myself, wouldn't have to buy office for mac in order to be able to use this software. The fact that you have a large choice of application types to save documents as is also a benefit; for an executive in a foreign country without internet access, they could use this instead of MS Office if there was a glitch in MS Office software and weren't able to download patch or whatever.
I'm curious as to what Microsoft thinks about this. I'd think that software companies that feel truly threatened by this would work hard to discredit it. On other hand, maybe this creates good competition and forces them to come up with better innovations...
Bottom line, mixed feelings on this one.