The power consumption of a network becomes a critical performance metric for a petabit-per-second scale Internet, in addition to the system cost. We investigate the power and cost efficiency of all-optical and electrical technologies to understand the design principle for petabit-scale hybrid optical switch nodes for optical packet and burst switching. In order to achieve an efficient hybrid design, we point out the interesting observation that the use of long packets switched by passive-medium photonic switches can substantially reduce power consumption and system cost. For contention resolution, shared electronic memory buffers are more effective and power efficient than fiber delay line buffers. An empirical optimization exhibits that a traditional all-optical solution is not the best choice for power and cost efficiency. Using passive-medium photonic switches with electronic memory buffers, we can introduce a substantial savings in power and cost, approximately half of those of commercially available optical cross-connect systems, with a packet loss rate as low as 10(-6).