I was initially skeptical of Colaboratory notebooks when it was first released, but the value of a free GPU (and Python 3 support eventually added) makes it worthwhile to use. I recently wrote a tutorial on training a text-generating neural network based on Colaboratory here: http://minimaxir.com/2018/05/text-neural-networks/ (and I have trained many-hours-worth of models with it!)

The only problem I have with the Colaboratory Notebooks is that file I/O is a pain in the butt (and requires Chrome).