I've noticed that some projects refer to gtest_main-mdd.lib and others to gmock_maind.lib in my Visual Studio 2010 setup and wanted to know what the difference between the two libs is?
Projects don't have to use both gtest and gmock but one might want to choose using gtest without gmock or vice versa. For either case you need a way to introduce the main function, hence you have 2 libs for introducing it.
Anyway, if you are using both then it's better to use gmock_maind.lib since it has an initialization for the mock framework and for the test framework as well. While gtest_main-mdd.lib initializes only the test part. Look at the gmock_main.cc and gtest_main.cc