Definitely IN! If you commit to a relationship you have to learn to negotiate. If you pull out, why should the other side bother to consider your issues at all?
Is this really the time to pull out of Europe and link with Russia, China, India, Brazil and Indonesia - all of which have economic difficulties?
AND some of these do not share our values e.g. equality of opportunity: human rights both in and out of the workplace: health and safety (example - someone's undergraduate son from North Wales who was working in China on his approved year out in industry was killed on a building site earlier this year because of grossly inadequate safety standards): and, not least, the protection of the environment.
I agree with Nandalot about the job losses which will be substantial if we exit.
I also agree with Maggiemaybe about electing a parliament to make informed decisions, and that the money could have been MUCH better spent - health, education, transport? - than on a referendum. The only reason we are being consulted at all over this is because there has been a split in the Conservative party.
And I believe that anyone who is dismissive about security issues in our unstable world has her head in the sand.