This is a basic disclaimer and realistically offers you no protection whatsoever, beyond the ability to say that users should have been aware who the content belonged to in a legal case or take down request. The UK's copyright service has this to say:-
There is no legal requirement to include a copyright notice. Whether a
notice is used or not will not change the fact that copyright exists
in the work. It is however strongly recommended that you include one
on your work if all all possible to deter copyright infringement.
As Stack exchange, for example, publishes only user generated content it's uses a creative commons licence. Given that your users will be publishing content too it would be wise to use an appropriate copyright/creative commons statement on the user generated pages while maintaining other copyright statement(s) for pages with content generated by your site's in-house authors.
It's also wise to be clear about who own's the articles, your site, or the author and ensure that there is correct contact information available for authors if they maintain ownership of a piece.
What data you collect and store about your them.
Where you store (Geographically), or where you send that data to be stored (Geographically).
Why you collect and store this information.
Who the policy applies to, or who different parts of the policy applies to i.e. you will need to differentiate between registered users and visiting users.
What they can expect to happen if they delete their account e.g. will all their posts be deleted or preserved.
To give you an apt example of Personally Identifiable Data many BBS and forum applications ask the user for their date of birth during registration, the software does this to automatically send the user an email on their birthday. This is really nice but it's now a very silly thing to do because storing that information requires them to comply with data protection laws in the country the site is hosted in.
This is why it's very important to know where your server is located and know what the local laws relating to storage of information are. You might have a UK based site, but your server may be in Germany. If you use a CDN the problem suddenly becomes much, much bigger.
The UK Information Commissioners Office use and reccommend this privacy statement. It's a bit of a minefield but you need to assess what cookie and tracking data is being stored about your users, this might include cookies set by Advertising Networks, Analytics software, session tracking, flash video, flash audio etc. Google Analytics sends a great deal of data back home to the USA, your users should be aware of this.
The names are largely interchangeable but this should indicate what users can and can't do, standards of behavior and so on. This question 'Are there any legal implications to reading a user's privates messages on a forum?' is a good example of why this statement is important on user generated sites.
You should make clear to your users:-
If, when and why they can expect to be banned from the site, for how long and what if any appeals will be accepted.
If and how you might report abusive or illegal activity to law enforcement.
If their private messages are in fact private.
along with anything else that might be pertinent e.g. discussion of illegal fishing may cause you problems.
Please note: I'm not a lawyer in any country, this isn't legal advice it's opinion.