EUobserver has reported that the Irish Government isn't being firm about the date of the referendum, to say the least. I'll take this opportunity to outline my thoughts on setting the date.
1. The guarantees must be agreed on, and have been laid down in writing. The polls showing a swing in favour of the Treaty ask questions based on the assumption that satisfactory guarantees will be, well, guaranteed. To put the Treaty to the vote without anything to show for the reviews and negotiations of the last year would be a major political weakness. The Irish people need to be offered something new, even if I don't believe the guarantees are necessary, apart from the one on the status of the Irish Commissioner.
2. There needs to be a clear run up to the election. All pro-Lisbon parties need to work together effectively in the next referendum - this means there needs to be a clear start, and a joint campaign launch. Keeping the date unclear could be damaging to the coherence and unity of the pro-Lisbon side even if it's intended to weaken the anti-Lisbonites.
3. Rule out May and June - and therefore April too. May and June will be taken up with the EP elections, and it will just be providing free publicity to the anti-Lisbonites to bring up the issue so powerfully so close to the elections. A win for anti-Lisbon candidates will strengthen the anti-Lisbon position when it comes to the referendum. For reasons of giving a good run up to the vote (and the reasons in 1 & 2), this also excludes April as a possible referendum month.
4. A good run up is needed. (Linked to 2) Obvious, in my opinion. The case for needs to be made clearly, and the contra side needs to have enough space too. There should be no snap referendum, like last time. A "no means no" and "they're bullying us" doesn't work quite so well if there's a good run up and a long debate. A longer debate would draw out more practical questions and get past all the knee-jerk no-ism. At least, that's my theory.
5. It should be as soon as possible, provided that the conditions above are met. July or August would be good, in my opinion. The government can be punished in the local and European elections, which may clear the political air of the need to punish the government (though I wouldn't underestimate this government's ability to enrage the public). The political air needs to be as clear as possible to ensure as reasoned a debate as possible.
So for me, July-September (and maybe October) is the best window of time for the referendum, depending on the political conditions. That's my current thinking, anyway.