In the year 2003 the MIT Technology review ranked "Grid Computing" among the 10 Emerging Technologies That Will Change the World .
We are now four years later and something is not going well with "Grid Computing".
An indication that there is a problem can easily be seen by looking at the "Google Trends" plot for the term "Grid Computing":
(click on the image to get the current trend).
This finding can be compared with another buzz word, "Virtualization", which is older than "Grid Computing" and yet is gaining more and more momentum:
There is however one exception. The Academic Grid is still having lot's of glory thanks to the huge heavily funded European (EGEE) and other US projects. When LHC data will start to be taken at CERN it will reach it's top importance. But, it seems that for other scientific projects Grid Computing is not going to be such a success. It will remain as "Nice to have" but will never replace High-Performance Computing (HPC) on one hand and classical distributed computing tools such as Condor  which exists for more than 20 years on the other hand.
Once the governmental fundings will be removed then all the hype of the academic Grid Computing will decline very quickly as well.
As was pointed in an interesting talk by Fabrizio Gagliardi about the future of grid computing, at the GridKa07 School, other kinds of Grid Computing infrastructures that will stand on stable financial ground may emerge as the successors, for example Amazon's S3 and EC2 and the joint IBM and Google's cloud computing.