I did typeset in masters thesis in ConTeXt. It worked okay enough, but for me, it didn't provide any features that make up for the increased time spent searching for stuff because there's less documentation and a much smaller community.

I also used it to typeset a project report which had some msword specific formatting rules. I found it more customizable than LaTeX in that regard, but I did have to read the docs a lot more.

I particularly like the fact that you can control floats much better than in LaTex/pdfTeX, but I agree that the community is smaller.

It appears that there is no development in ConTeXt for a while now. I haven't checked it, but it seems that they are working on LuaMetaTeX.

http://www.pragma-ade.com/luametatex-1.htm