I've been doing this a LONG time...
At first I used to read all the dev sites and attend conventions, but at some point you can only focus on so many things.
Now I only follow languages I can write in. I tried RoR a few years ago, when it was hot and found I could do everything I needed to do better, with Python, PHP and JS. So what do I need it for?
I read HN, Reddit, go to some meetups, wired and some blogs are good too. But I mostly just learn new stuff when I need to.