Opportunistic Spectrum Access (OSA) is foreseen as the future of wireless communications. However, today's cognitive radio technologies lag far behind the OSA goals and do not allow for the applicability of exiting theoretical distributed OSA techniques. In this paper, we experimentally demonstrate the ability of realizing OSA despite the practical limitations of existing transceiver technologies. We use the general purpose Wireless open-Access Research Platform (WARP) to instrument the implementation of fundamental OSA functionalities. Then we implement a suite of OSA schemes using this implementation framework. Our experiments show that suboptimal but practical OSA approaches such as random spectrum sensing and non-greedy access achieve superior performance given cognitive radios with limited capabilities compared to OSA approaches that are optimized for fully-capable cognitive radio networks (e.g., with wide-band sensing capability and adopt winner-takes-all access relying on network-wide coordination mechanisms).