I do my best to evangelize ChromeOS. But I always try to make sure that people understand what they are getting and what they are not getting.
I really enjoy ChromeOS and my Chromebooks. But at the same time I am not some complete over-zealous fanboy that tries to turn ChromeOS into something it is not.
Example: if you need to edit (on a professional level) large, locally stored, video files and you are wondering if you should buy a Chromebook to do that, I would say no.
Example: you need a new computer and you mostly need it to communicate with friends, family, and colleagues via gmail and social networks... You need to be able to create docs, presentations, and spreadsheets... You need to access the web for shopping (Amazon, eBay, etc) and entertainment (Netflix, Hulu, the PlayStore, etc) - I would definitely recommend a Chromebook.
For 80% of people a Chromebook is going to do 95% of what they need to do.