SaaS in real life

First of all, I think SaaS (Software as a Service) is a great idea, but if the user experience is to be comparable to a client installed application it has to be at least as quick and at least as flexible as an application. I work quite a lot with collaborative solutions such as Sharepoint, and if I should suggest to use an online text editor or a spreadsheet, it would need to have the same integration and collaborative features as Office 2007. However, I have some difficulties imaging this feature rich integration from a SaaS, unless Microsoft joins the game.