My first thought, upon reading that British forces could be in action in Libya as early as Friday (http://www.bbc.co.uk/news/politics/) was 'if that happens I will have to leave the Lib Dems'. Regular readers (all three of you) will know about my strong anti-intervention stance.
Also, I have often considered what the Lib Dems could do that would make me leave the party, and although I haven't decided on a definite tipping point, I always decided that if the UK went to war without very good reason while Lib Dems are in government I would leave. No matter what compromises the party has made, they always have, over Labour, the fact that they were the sole opposition to a long, disastrous, bloody and expensive conflict resulting in up to a million deaths. I can't keep arguing this if the Lib Dems have been involved in an invasion too.
Generally I believe that foreign intervention is not the business of countries like ours, particularly with our disastrous track record in Africa and the Middle East. I think even with good intentions and in the absence of ulterior motives, the outcome is almost never good for the victim country.
However, there are some differences between this conflict and Iraq, for example. Firstly, it appears that if action is taken it will be internationally agreed upon with UN resolutions. Secondly, a no fly zone places a clear demand on Gaddafi, the like of which was never placed on Hussein. And thirdly, it is a country already engaged in a bloody conflict. Iraq was a stable nation with working infrastructure that was destroyed by invasion. Libya is already in civil war, so the purpose of invading for regime change is not as clear-cut. There is an existing conflict we would simply be taking sides in, rather than creating a new conflict.
Ultimately, UN sanctioned military action is much more acceptable than random invasion, and the fact that there is already a conflict clearly come into it.
I suppose my decision of whether or not to remain in the party will come not through whether or not British troops go into action, but whether or not they do so legally, and if the conflict is resolved quickly and efficiently with maximum autonomy for the Libyans, a proper leaving strategy is decided and a stable democracy is left, not a corrupt puppet regime.
I will probably not immediately leave when invasion is announced, but I will seriously consider my position depending on the manner in which the invasion is conducted as well as its duration etc.
Since writing, the UN has passed a resolution calling for intervention but not invasion (http://www.bbc.co.uk/news/world-africa-12779628). So far this appears to have been well-handled. The prospect of Libya returning to Gaddafi's control is very real and extremely undesirable, so if UN powers can aid the rebels without invading this does not seem too objectionable.
What is interesting about the story is that Russia and China abstained on the vote because they believe military intervention sets a dangerous precedent. Firstly it seems worrying that the West, which usually tries to claim the moral high ground, is always so much more keen to enter into armed conflict. Secondly we are very lucky as a planet that China and Russia take such a responsible attitude to foreign intervention (although I question Russia's commitment to this due to their frequent conflicts with their neighbours), because if they had the same arrogance in their political systems that the liberal democracies do, they would surely be seeking to impose communism or whatever warped quasi-democracy Russia has on the rest of the world.