We have migrated to Geo::Calc::XS, and ASP, the author of Geo::Calc and Geo::Calc::XS, has kindly allowed me to be a co-maintainer of Geo::Calc::XS. Note that Geo::Calc::XS isn't a drop-in replacement but it almost is.
Geo::Calc does what it says on the tin, but the documentation does leave a lot unmentioned. There should be at least a mention of Geo::Calc::XS and what the differences are. Some of the documentation is actually incorrect, for which I've filed a bug.
The object-oriented interface is not to my taste, but it's easily understandable.