Real-time ray tracing is currently a no-no for games because of performance constraints, but as the parallel processing race heats up, more and more folks are taking a second look at the rendering method. Intel, for one, called ray tracing "the future for games" last year, and it even hired the developer of ray traced versions of the Quake game engines in April.
However, Beyond3D has published an article entitled "Real-Time Ray Tracing : Holy Grail or Fools’ Errand?" that makes an interesting case for why ray tracing might not be a good choice for games. The article's arguments against ray tracing include antialiasing, which is difficult and costly to do in a ray-traced engine, as well as potential performance issues with large dynamic scenes, poor lighting quality in diffuse scenes, and difficulty simulating nonlinear subsurface scattering and indirect refractions.
The author concludes that, at best, a real-time ray tracing engine would "only produce comparable image quality to current rasterisation-based renderers unless the scene is highly reflective and refractive." Beyond3D believes ray tracing isn't the holy grail of game rendering, and that hardware makers and programmers should instead work toward a good real-time rendering system for indirect lighting.