About the salt, my mum sent me a book off amazon only just published, and the author says that from what research there is on various cravings, the thoughts are that salt is craved because of all the extra fluid being produced by the body e.g. for amniotic fluid and your extra blood pumping around. You need more salt to make all the electrolytes work so that nutrients can pass through cell walls.
I also read (different book I think) about natural vs managed third stage of labour. Didn't think about that at all first time round. I might put in my birth plan this time that I don't want the cord cut for a few minutes - if baby is put on mother's skin and starts rooting for the breast straight away (as they do) you get a couple of minutes where a significant amount of blood drains from the placenta to the baby (which is good because they then don't need to make so much of their own blood supply) and also the suckling stimulates the hormones that tell the uterus to let go of the placenta, which is what the syntocinon injection in the (mum's) thigh is for in the 'managed third stage'. The risk with natural third stage is that the uterus doesn't know when to stop letting go though, and could turn into a primary postpartum haemorrhage. I also now realise from this that I should have been recorded as having had a secondary PPH because the 'light' bleeding after birth went on for six weeks until I was given antibiotics. Still, that might be something to discuss when it comes to birth plan.
I think the difference between antenatal classes, if you have the choice, is that the children's centre and maternity unit classes are very much "this is what we have to offer, this is what we usually do" whereas NCT and independent groups will/should be more about "these are your options, you'll be offered this but remember you could ask for that, here's how to ask them to present it in terms of real risk rather than relative" and so on. I think healthcare professionals, wonderful as the vast majority of them are, sometimes don't have the time and capacity to help patients to be informed 'clients' - if you just teach someone how to question the advice they're given, they could just end up arguing the toss over everything, so you create more work for yourself! But if you can help them make informed choices in partnership with their HCPs, everyone's happier and better fulfilled by the experience and the service, if you see what I mean.