Care to comment on the reasons for using ConTeXt versus LaTeX? I've been curious about ConTeXt for a while, but I fall back on LaTeX out of familiarity (and the need to use provided document classes.)
ConTeXt is excellent if you care about design -- visual, layout, use of non-traditional typeface families, non-traditional print medium, create magazines, glossies, etc.,.
Writing a new style, class etc., for LaTeX feels like it's for "experts only". On the other hand, extending and creating new styles etc., for ConTeXt is much more natural part of creating the document.
ConTeXt is also highly programmable and extensible using Lua, XML(think machine generated catalogue).
With Metapost (graphics language), you can create highly sophistical vector diagrams. I have found pgf/tikz to be highly opinionated and it take much more upfront learning compared to metapost.
ConTeXt is also more intuitive, IMHO.