The impact of health information on the web is mounting and with the Health 2.0 revolution around the corner, online health promotion and management is becoming a reality. User-generated content is at the core of this revolution and brings to the fore the essential question of trust evaluation, a pertinent problem for health applications in particular. Evolving Web 2.0 health applications provide abundant opportunities for research. We identify these applications, discuss the challenges for trust assessment, characterize conceivable variables, list potential techniques for analysis, and provide a vision for future research.