Optical burst switching (OBS) has been proposed in the late 1990s as a novel photonic network architecture directed towards efficient transport of IP traffic. OBS aims at cost-efficient and dynamic provisioning of sub-wavelength granularity by optimally combining electronics and optics. Optical bursts cut through intermediate nodes, i.e., data stays in the optical domain at all times, while the control information is signaled out-of-band and processed electronically. In contrast to optical packet switching, OBS aggregates and assembles packets electronically into bursts of variable length according to destination and QoS class at the edge of the network. This paper surveys current trends in OBS and discusses proposed solutions for burst reservation and scheduling, burst assembly, contention resolution and QoS provisioning as well as design and scalability of OBS nodes. Also, it looks at the question of the optimal burst size, which has been around from the very beginning of OBS, based on recent trends and results. On the one hand, burst size and burst characteristics are influenced by client layer traffic and burst assembly scheme. On the other hand burst size and burst characteristics have an impact on network performance and node architectures. Finally, consequences of burst durations in the microsecond and millisecond range are presented and compared.