The emergence and implementation of advanced smart grid technologies will enable enhanced utilization of Plug-in Electric Vehicles (PEVs) as MESS which can provide system-wide services. With significant penetration of PEVs in the near future, the concept introduced in literatures as Vehicle to Grid (V2G) will be practically possible. The V2G concept eases the integration of renewable energy resources into power system and gives a new force to the inevitable move towards power generation by clean energy resources. Therefore, trends in utilizing energy stored in PEVs will bring undeniable economic and environmental benefits. The V2G aspect has been the field of many research works in the last few years. This paper intends to present a study conducted to reveal the different features of V2G in power system. In this study, V2G applications are investigated from the perspective of power system as well as electric market. In addition, V2G capabilities are discussed to utilize renewable energy resources as secure power sources and to provide ancillary services. Specifically, the paper has detailed the importance of smart parking lots, their opportunities and challenges in relieving V2G difficulties and improving its utilization. In order to clarify different issues, the authors present practical analyses which are results of a loss optimization problem in a residential power grid. From a realistic standpoint, this work has tried to identify the major barriers towards making V2G practical and addresses remarks which will make V2G concept feasible as fast and simply as possible.