Growth of (Idle) Computer Processing Power
Second driving force has been the enormous amounts of untapped processing power all over the world. Take the SETI project as example again; they recognized the fact that consumers today have one or more PCs in their home, of which most are doing nothing but wasting energy and processing capacity. This realization could have great consequences for organizations, which invest millions of dollars into IT equipment each year.
Realization of the unused processing power of idle resources in companies has led to the renewed interest in grid computing. Increased focus on efficiency and effectiveness with currently owned assets has rekindled the interest in grid computing.
Willingness of groups or individuals within companies to share resources bought with their own budget.
A large initiative to realize and act upon unused processing resources is Distributed.net. Through distributed.net clients encryption is tested for robustness by using idle processors on computers around the world.
With regards to timing, all we can really say is that this type of approach to computing has only been really become possible with the Internet becoming mainstream, and consumers acquiring computers which have more processing power then they need for their every day jobs.