I do believe this to be one of a handful of such sites in South Africa, although I service clients from every country in the world who need English language proofreading.
A few things have inspired me to offer this proofreading service, not the least of which is that recently I have noticed more and more errors creeping into posts made in the social networking arena. Previously, most grammatical errors on the web were to be found in comments left by Youtube users, but more recently, with the advent of Twitter, grammatical errors have become increasingly more common, and this is very offputting especially when they reflect under the names of business owners. It gives off an unprofessional feel - and this is a problem I hope to be able to alleviate. Why not dictate or write all your social media comments down and send them to me to either proofread, type and proofread or transcribe and proofread? Doing that will save you time as you won't have to visit so many social network sites, and ensure that your spelling and grammar is correct, thus making a good impression on potential clients.
One of my pet hates is incorrect usage of the apostrophe and it seems many people don't know, for example, that 'their', 'they're' and 'there' all have different meanings. It's even worse when 'your and you're' are used interchangeably. If you have misused these, any knowledgeable client will pick this up and be put off using your services.
If anyone has any particular questions on grammatical style, feel free to contact me with these as well.