Blender Version: 2.69 official release (Linux 32 bit and Windows 64 bit)
How to reproduce: Create hair particle system, switch mode in 3d view to "Particle Edit" and viewport shading to "Rendered". The hair is rendered as halos, and not strands. Problem persists even when solid material is applied to emitter.
This seemed like a very conspicuous bug, but I couldn't find it in the search function. I apologize if this is a duplicate report.