[ben_jones]

It is an industry that goes way beyond Twitter and PR companies. It's incredibly popular for US businesses to pay firms in Asia, Africa, etc. to trawl social media and collect data using various automaton tools for BI and other purposes.

That said I also believe a lot of trolls and political posters are just normal people voicing their malignant opinions to the point where it is nearly impossible to identify astroturfing as long as the accounts are "tenured" enough (real pictures, some age, etc.).