It seems that we are not only comparing web based office suites, but also the platform giants - Google and Microsoft.
Since the explosion of 'collaborative office based suites' (such as Google Docs, Zoho and ThinkFree) Microsoft have since launched their own collaborative office version called 'Office Live Workspace'. Whilst there have been many comparison reviews on Google Docs V's Office Live, Google Docs appears to come out on top when it comes to the collaboration features. However, some users may prefer using the familiar MS Office interface.
Whilst the debate over Google and Microsoft continues, I think Google Docs should pay more attention to the competition from the new up and coming collaborative tools online, such as Remember The Milk and Seesmic.