Am in a bit of a strange position (but that's my sex-life for you) and am also in a bit of a strange position in that, despite being heavily pro-union, I've never had the opportunity to be in one mainly because I used to be one of the much-derided 'Public Sector' workers.
A couple of things really wind me up about this type of debate. Firstly, the "oh, it's always the Public Sector workers that cause a fuss"... mainly, iit's because they have a tendency to get shat upon from the greatest of heights because those that employ them know that a vast majority are motivated more by a sense of duty than money (why else would a Nurse work in the NHS rather than BUPA, where people very rarely spit at or punch you, or if they do, it's a far better class of spit).
The other facet of this is the "Well, why did you sign up then?". Maybe, just [Poor language removed] maybe, they signed up to do a job that they felt made a [Poor language removed] defference.... their reward for this shouldn't be having to smile while they get crapped on, they should have a means of making their point.
Another point of note is the distinction between the Public Sector (ie all nationalised concerns) and Public Services (Police, Armed Forces, Prison Service) who are not allowed Union representation having Federations, Assocations, or [Poor language removed] all, and whose rights to withdraw labour are limited to 'Working to rule' or going to jail.
Personally, I don't see the Royal Mail situation as a Public Service issue, it has Private competitors in the market place. One of two things will happen.... either private mail will increase in price to reflect it's market value... probably Pete's £1 for a first class delivery (there's your market forces) or the government will end up paying DHL, RM et al a subsidy to be able to employ staff on a competitive wage, while maintaining the artificially low cost of mail (like how the railways were supposed to work.