I am talking about tight integration and not web mashups created by writing a web application wrapper for other people's web services. GMail and Google Calendar integration looks promising at this point, but we will have to wait and see how far it goes. Even though I wrote my own web based wordprocessing web app (KBdocs.com) I am still a little skeptical about how widely used web based document processing will be.
Anything that challenges Microsoft Exchange/Outlook integration, but implemented as a web application looks really interesting to me. Because of privacy and IP protection concerns for corporations, I think that an appliance style product for combined search, email, and calendaring would be a great business idea (hey, anyone want to start a company :-)
I expect to see the costs (development, acquisition, downloading, deployment, maintenance, etc.) of infrastructure software to continue to be squeezed lower. Priced Exchange licenses lately? :-)