people often make negative comments via social networking sites. I believe a publicly viewable site is not an appropriate place to criticise the manner in which someone does their job. There are appropriate places to register complaints, but it certainly isn't twitter / facebook etc.
I disagree completely with this. I think raising complaints in a public forum is exactly the appropriate place to do it. Raising things publicly means the company looks into it properly, rather than dusting it under the carpet like they do with so many complaints letters.
Take my gas company. I'd been arguing with them for months about a gas bill, and tweeted about it in frustration. It was fixed that morning. Doing things publicly gets their attention; private letters do not.
If any member of a company's staff (and this goes beyond railway staff) is getting hauled over the coals because of a tweet about them, and with no other evidence, then that is a management failing. You should raise it with the gaffer. But I don't see what's wrong with Twitter enabling complaints about service provision, even if a good proportion of those complaints are weapons-grade bollocks.
I'm not sure where abuse comes into it either. Swearing at the twitter staff is wholly unacceptable, but I don't see very much of that at all; when it happens, the twitter staff normally deal with it well. Look at London Midland's feed as an example of how to do it properly. But most people are just sounding off about the fact that, yet again, their FCC Thameslink train is ten minutes late and short formed.
The only benefit to in-cab CCTV is retrospectively, to find out what happened if an incident did happen. But that can usually be determined through other means, or through the use of black box recorders like on aircraft. Drivers doing things they shouldn't happens- just look at Southall- but installing CCTV seems a bit like overkill for what is a very rare occurrence.