Does the Services module implement caching on GET requests? Before I build a REST server with the Services module, I'd like to know if the responses to the GET requests are being cached? I searched Google and it seems that caching wasn't implemented, however, those articles are from 2011 and 2012.
No, the Services module does not support caching on GET requests:

http://cgit.drupalcode.org/services/tree/resources/node_resource.inc?h=7.x-3.x#n253

As you can see, each time the resource's callback function is invoked, it makes a call to node_load(). You can use the Services API to preprocess/overwrite the resources to implement caching though:

http://cgit.drupalcode.org/services/tree/docs/services.alter.api.php?h=7.x-3.x