I am currently the publication chair of a ACM SIGCHI conference and actually all the work is managed by by Sheridan publishing for ACM. The process is really streamlined. The main paper track actually is now a journal since a few years, so it is mostly getting the flea circus of 30 workshops and other adjunct papers to meet their deadlines. We are still under the old syste, so I wonder what the effect of the new system will be as some universities prepay the fees, while others require the authors to do that per paper afaik.