Still leaning on iMacros as a go to solution for simple web automation. Nothing is easier, and while you might need to solve some challenges such as proxy rotation - it's free so how can you go wrong?
Just set up a few firefox profiles, create some CSV files with the contents you want posted and you are in business. Will this take you a while to figure out? Sure. Is it worth the time? I guess you know what you're trying to do, so the answer should be pretty obvious. No need to screw around with other non-working or convoluted methods. Posting content to a website by CSV file using iMacros is so easy a caveman could do it. I bet you could have your own automated solution put together within 3-4 hours.
With a little more effort I bet you could easily implement a content spinning solution as well. I envision a php script that runs by cron and automatically generates the contents of the CSV files used by the imacros, but that might not even be necessary depending on your implementation model. Good luck with whatever solutions you choose for this!
