Not much - some interesting points about how strict any fiscal union (which would be a requirement of currency union) would have to be to be remotely acceptable. Basically making the point that because of the relative size of Scotland's economy relative to the rest of the UK there would be an asymmetric relationship where rUK could support Scotland, but Scotland couldn't support rUK (if the economies were diverging.) That seems to be part of why it's being opposed. The fiscal controls that were meant to prevent that situation in the Eurozone weren't enough so they would need to be so unbelievably strict that it would be pointless. Plus complete lack of political will.
Lots of chat about the how sterlingisation (aka using the pound without union) wouldn't work, would leave us vulnerable, inability to set our own interest rates etc. They suggested that, as I suspected, the impact on oil is quite strongly considered in current BoE decisions. They were also quite strong on how bad not having a central bank would be for the financial services industry - basically said it was the worst possible option and we'd be better creating our own completely separate currency than doing that. Which I'm very much inclined to agree with tbh and nobody at the talk argued either.
Also points about fiscal transfers i.e. different parts of the UK contribute more or less at different times depending on how their industries are doing. The recent oil price falls apparently meant that Scotland's "contribution" went down by something like £1.2b compared to what was expected but actually our budget went up. There are other times when it's the other way and we support other areas more, but the ability to do that creates a strength and stability.
They said that even in quite "federal" countries, there's normally at least 25% GDP which is communal (my word not theirs!) and that helps to maintain stability.
Hmm, what else...
There was analysis done where the white paper was costed up
I'll leave you to guess the outcome of that!
DOn't get me wrong, some of it was a bit rubbish (they mentioned the NHS as a UK institution which sent everyone's eyebrows off the scale!) but I don't think their economic analysis was too far out.