I can provide a data point here. In college I did some App Engine development. At a previous job, we used open source Google Java libraries like Guice and Guav

I can provide a data point here. In college I did some App Engine development. At a previous job, we used open source Google Java libraries like Guice and Guava. I recently started at Google and walked in the door largely proficient in using their stack. In my opinion, they did everyone a favour. They've done good by other companies by providing them with solid libraries. They did right by me -- knowledge of their libraries presumably made me a stronger candidate. Finally, they did right by themselves by reducing the time it took me to get up to speed.