Back in the days I was actually doing some campaigns for companies on Wikipedia. Those would be based on creating high quality content and adding link to our customer in exchange as a source (we were placing nice article on customers page researched by knowledgeable folks from uni). We were doing a lot of work creating pages, adding really nice content. Some moderators knew about our actions but they were cool about it as they liked content we have been creating.

Because of how many edits we were making (at least 20 a day) we have witnessed politics and lobbying on Wikipedia. The worst are unfortunately subjects that could by any extent critique US, UK, French or Russian governments, history, monopoly or news.

We have seen highest placed people with absolute power just removing any content without reason and blocking further changes.

One day I got in to the conversation with one of the "untouchable" - admin with small amount of edits etc but for some reason high in ranks. I got in to argument as he removed 500+ words improvement of pretty dead article about some delicate subject (heavy industry related) - this included removal of some links to large companies (they were unrelated though and we placed in exchange links to government institutions and few scholar research). Argument was something like "I would like you to let us know the reason for removing our edits." after no answer for 7 days I sent "If we wont get answer within 48 hours we will be forced tp take this case up as reverse seem as selfpromotion".

Result - around 2 thousands quality edits removed (we had probably links to our related article customers on only ~200 edits). Complete removal of our accounts, blacklisting WHOLE IP ranges from our office and probably hundreds of other regular users. That is how Wikipedia is neutral...