When I have the time I will occasionally tab out a song that I would like to know how to play to strengthen my ear training skills, but aside from that now i rarely learn whole covers since I already have learned many. And instead I am writing material for my own album :)
I learn the parts of songs that I like the most so that I can see how they did that. Many of the intricacies of writing solid riffs comes from the rhythm of the riff, and listening to it one can easily learn to emulate the rhythm of what the other player is doing. Learning all seven modes has allowed me to stay in key all over the guitar neck and invent my own riffs on the spot. Just a few pointers ;)