That's what I said three years ago when I bought my G5 DP and there is no sign of it slowing down.
The OS and software vendors are constantly creating fatter software, not leaner. They are making it do a lot more and taking advantage of the power. Somebody posted about only audio and video people taking advantage of it. Well, the truth databases are quite capable at utilizing as many cores as a business can afford as well as many CAD functions, a lot of CAE and even some CAM.
One thing I've dreamed about for a log time is having one central computer in a house that would be powerful enough for everyone to use. Hmmm, sounds like a mainframe, doesn't it? I would love to administer one computer with all the user accounts instead of four computers, each with all their own copy of the OS with all its issues, security problems and incompatibilities. Not to mention the myriad of software and all of its shortcomings too.
16 core? 64? 512? There is research being done with computers consisting of many low power processors and the early results are very promising.