Cameron has promised an EU in/out referendum by the end of 2017.
It has been made clear (cast iron not withstanding) that there will be a period to negotiation to come to a new 'settlement' for the UK in the EU (whatever 'settlement' means or entails...). Then the UK population will be given a referendum to either accept the new settlement or to 'leave' the EU (whatever 'leaving' means or entails...).
It has also been said (and I think this can only be taken one way) that this in/out referendum will take place before the end of 2017 - although it is still not clear who will be allowed to vote in this.
Nothing has been said about what the government will need to do in light of the referendum result - usually the EU would re-run any referendum that didn't give the result it wanted - so if the vote was 'out' what would happen? When would UK actually be out?
So even this far there is great doubt about what is actually meant...
But further - one of the EU presidents (there are three presidents, each of a different function) has already stepped in to tell Cameron to 'respect the EU rules on such things' - odd as no one knew there were any EU rules, and certainly didn't think the referendum was any business of the EU (http://www.theguardian.com/politics/2013/jan/23/david-cameron-eu-speech-referendum) so they are interfering already!
The big issue I can see is that treaty change in the EU takes years... there is absolutely no chance of Cameron getting the EU to change any treaty (needing agreement of *every* member) before the referendum - so all that could be offered at the referendum is a *promise* of changes... The promises will be empty, leaving total wiggleroom, so they can promise *anything*.
Remember a UK parliament *cannot* bind a future parliament - Cameron has said he is not going to serve another term so come 2020 anything not finalised can be abandoned(!).
Watch this space!