Citrix is acquiring XenSource (http://www.eweek.com/article2/0,1895,2171251,00.asp). Very cool.
As grid computing becomes reality and as processing power, memory, and bandwidth become utilities just like water and electricity, I see that the future lies in virtualization technologies + remote X sessions and/or VNC.
I see that the future in creating an online and pervasive workspace lies on running multiple operating systems and offering it as a service. Each user can have his own virtual machine, and each user can pay the provider based on his memory and processing requirements for each session.
This will be the killer app once the infrastructure is in place.