Here’s an interesting find in the Google results. It may be that it’s just a test, and may not be rolled out permanently, but Google appears to be labelling websites which are slow to respond as just that: “Slow”. This appears to be the original observation.
Google is already thought to “penalise” sites in the results for being slow, but with these labels it probably wouldn’t need to do so. That’s because another factor in its rankings appears to be the clickthrough rate on a result, and I’d expect that any site getting the dreaded “Slow” label would see its clickthrough rate fall. Just a guess.
Is this a problem? I suspect it’s unlikely for most companies, although I’d be happy to see certain manufacturers’ websites penalised in this way, if only to wake them up from their complacency in using a content management system which clearly can’t cope. You can test out your website using Google’s PageSpeed Insights tool, although please don’t panic about the long list of improvements it will suggest, as most are usually quite obscure. If you have a good website developer who won’t charge the earth for fixing things, feel free, but don’t worry too much unless your score is well under 50%.
Another tool worth trying is Pingdom’s Website Speed Test, which gives you lots of useful information, and tells you how your site compares to an average of all its tests.