Responsive web design is something of a current fad for brand sites. Some people will tell you it is the ONLY way to develop. However, as with all things technology, the tool of choice should be a strategic one – what is the brand trying to achieve and what is the best way to deliver it? Responsive design is great for some things, but it may not always be appropriate. A large eCommerce site, is a good example of where responsive design is problematic.
The approach will also impact on SEO. eConsultancy have published an excellent article on the considerations of mobile design on SEO (see diagram below):