Actually, companies like Netsuite and Salesforce.com were there first but Google perfected the mass market play. A posting on The Stalwart describes Google's approach best. Here's a quote: "In Google's vision, all of your important data, and the software required to use it is centrally housed, accessible via a browser on any device--aka a thin client."
Microsoft's vision of rich client innovation is polar opposite to Google's. So when I returned to the office I was pleased to read about Microsoft's Windows Live and Office Live announcement. There's a ton of coverage about this on Tech.Memeorandum but the most insightful analysis is at the Microsoft Monitor Weblog in a post called - "What "Live" Is" and "What Live Is Not"
Microsoft Live is excellent news for the future of software and for enterprise/small/medium businesses. It's also a great strategic move by Microsoft.