Ask HN: Current hosted document editing/sharing systems and their direction?

I'm looking at a start-up opportunity (within my existing small company) based on connecting to existing hosted document systems such as Google Docs, Zoho Writer, Zimbra docs, buzzword.com, etc. (including photoshop.com for pictures, etc.) I guess there's also whatever Microsoft does with Office Online. (Are there other major such services I'm forgetting?) This might sound naive, but how would one go about figuring the relative popularity of these kinds of services and their trajectories? These kinds of systems are clearly gaining momentum, but one rarely hears about them in the day-to-day noise of the webosphere. Do you think they're headed for (mostly) replacement of the desktop-based office suites? Or will the desktop-based suites fight back and maintain some market share long-term? Or is classical online document editing going to fade away in the face of other collaboration methods like wikis? (I don't think so, ultimately, but it's certainly possible.)