Report - 30 day online visa extension in Bangkok
I used this service to extend my stay in Thailand (I was applying for Non O which requires a mininum of 16 days left on your stay). I only had 15 days left, hence the necessity to extend for 30 days.
The program is run by VFS, they charge 500 baht for the regular service and after you submit the forms online and get confirmation you go to Immigration Changwattana 3rd floor to get the stamp. It's in a VIP area with no waiting. Its managed by the VFS staff not Thai Government staff.
The service was great. I was greeted by the English speaking manager who told me at the moment they only have around 5 customers per day. She also said they were negotiating with the authorities and it was likely they would offer a similar service for other Visa types in the future.
Edit: Laksi Sqaure 30 day extension is only for Visa exempt entries. Entry on tourist visa extensions are still done at Changwattana