the field of supercomputing has undergone a significant paradigm shift in the last decade or so such that it used to require highly specialized hardware and designs. a supercomputing company that embodied this approach is Cray supercomputers.
however a new concept/trend has emerged that extremely high performance can be achieved with "off-the-shelf" components such as those used in consumer electronics and heavy internetworking using standard networking components. supercomputer designs have always utilized a large amount of parallelism but this trend has been amplified with the proliferation of the off-the-shelf type approach. also parallelism is much more being supported with sophisticated software architectures such as MPI, MapReduce, etc
so the systems are still highly parallel but the particular means of achieving that parallelism has shifted in the hardware and software. the parallelism is more visible at the application layer and not abstracted away.
also recently power consumption has become much more of an issue and supercomputers are starting to focus on energy-efficient designs and low-energy CPUs such as those used in mobile computing.  is a nice ref on key issues in current trends/barriers on high performance computing scalability.
 Next-Generation Supercomputers Kogge