I have spent my 17 year career working in a variety of roles, all of which technical to a large degree, both in the UK and internationally. During the last 7 years I have worked for, owned, consulted to and been consulted by, design and marketing agencies.
I work exclusively with a small number of marketing and design agencies in London and the South of England on a consultancy basis. For these agencies I provide tech support and system troubleshooting, search engine marketing, complex web building, pricing/presentation/pitching services and a lots more besides.
One of my key strengths is in winning pitches with agencies, especially for complex sites and digital marketing. A huge on-going benefit to my clients is that I can deliver the areas of the project the agency does not have the internal skills for, allowing them to concentrate on their key strengths and making clear profits.
Like my clients, I charge hourly and I have no minimum or maximum amount of time you may use. If you just need and emergency fix to your clients web app or server for a couple of hours thats fine, or you may want a longer term contract to mirror yours or your clients requirements no worries.
Many people ask if I do speculative work which I'm afraid the answer is no to, unless you are an existing client and have a very specific case.
I never disclose the agencies I work with either online or verbally. In many cases I work alongside my clients acting as one of their team and whilst I naturally need to promote my own services I don't do so at the detriment of my clients relationship with their clients.
The term was, as far as I know, coined by Wired in 2008 to describe a new type of 'techie' who goes one step further than the code to think up and implement innovative solutions to internet business requirements. A better description than I can come up with can be found here.