I have owned a Cougar PC for around 4 months my opinion is this:
1: Top quality build & components, vast range of customization options and quality components.
2: Faultless customer service, when you need help you get to speak to knowledgeable staff. The email replies can be slow (but a lot of places are like that now) so I would say that it is always best to ring them, that's what I do and I cannot fault them.
When you see inside a Cougar PC you can see that their system builders take great pride in their workmanship as the tidiness is excellent.