They make great autocompletion engines, most of the time. It's nice when it can recognize that I'm replicating a specific math formula and expands out the next dozen lines for me. It's less nice when it predicts code that's not even syntactically valid for the language or the correct API for the library I'm using. Those times, for whatever reason, seem to be popping up a lot in the last few weeks so I find myself disabling those suggestions more often than not.