This post is not about if or when we should automate the Look & Feel aspects of the product. This post assumes you have done the discussions, evaluations and validations required to reach the decision that, yes, we need to automate the Look & Feel of the product under test.
The next question is - how? What are the alternatives of accomplishing this type of automation?
If you need basic validation, there is an open-source alternative - where you can do Visual Testing and Validations using PhantomCss. Vishnu & Shridhar spoke about this in vodQA Pune - Innovations in Testing. See the slides and videos from their awesome session.
If you need more flexibility and functionality from the Look & Feel automation, and want to do this for cross-browser / multiple devices, then I recommend you look at Applitools Eyes product. I had have seen a couple of demos from Moshe and Adam about this product - and they were kind to record one of the demos and allow me to share it with all - you can see the demo here on youtube.
Applitools has a free account for individuals, with of course, certain limitation in usage (not functionality). You can sign-up for your account here and try it out.