Sometimes, it's hard to decide who exactly uses these message boards. Who are these people, and should we take them seriously? I suppose that anyone who has gone to the trouble of logging on and posting to any football message board must have at least some love and knowledge of their club - so why are some of them so vitriolic in their condemnation? But then, everyone is entitled to their own opinion.
Going online to a messageboard is a bit like finding out that the new guy in work is a big City fan - at last you have someone to talk to, and someone to bounce opinions off. But it's still banter and bluff - no different to a chat in the pub.
I don't believe that many clubs take the slightest bit of notice of fans' message boards. They have much better things to do, and anyway, it would be a full time job, for the poor unfortunate sod given the task. Someone at the club may well browse occasionally, but they were going to do that anyway - they have the same interest, after all.
The turnover of managers is down to the same old things - results firstly, and money a very close second. Poor results hit gates, league position, and eventually sponsorship. That's why managers get sacked - not because some guy on a message board doesn't like the way his team plays. The way his team plays may well be the cause of those poor results, but it's the results that cause the manager's departure - not the guy on the message board.