i know that ian duncan smith post is boring, but he is the tories expert on welfare, and i'm sure his figures are well meaning and add up.
Its not like scotland will be joining a booming EU after independance or be pulled along by the US. I trust alex salmond with running scotland but i don't trust him with this dice role. There is an immediate and big shortfall in his budgets, and based on what happened with the scottish parliment (let alone RBS) i bet he will borrow, banking on growth that is not out there right now.
The SNP majority will keep him in power for 15 years at the very least, it would be much wiser to be looking at a situation where scotland IS subsidising the UK stably for a period of years. If he's so confident about an independence he should be able to achieve that first, rather then walking into the imf with a set of badpipes and hoping it will all go well.