Technically, I implemented some of that stuff myself because I needed REST client that would work with PCLs and be a bit 'nicer' to use than just juggling strings/routes everywhere, so using annotations and wrapping Microsoft's HttpClient was obvious and relatively easy way out.

Anyway, I'll probably just phase out my own solution and start using the library.

[EDIT]

After checking it out, RefitStubs.cs file seems a little bit clunky, but the library as a whole looks solid enough. I'll look further into it.