Well you've heard all the negative news! So I thought I'd say some more positive things (and I'm not disagreeing with what others have said, I just don't want you to lose all hope!)
1. Is your husband's job fairly generous financially? Presuming that it is then you can afford to give Shanghai a try and if it doesn't work out you can afford to return to Australia. Can you take leave from your job and then decide after you've tried Shanghai?
2. You don't give details of your career but would it be something that would be likely to land you a job? I ask because I know that I personally spend all day in airconditioning at work in summer. Would that help your skin?
3. With regards to the other allergies/hayfever etc it might not be as bad as you are thinking. I get hayfever in Australia but have no problems in China...obviously it isn't pollution that causes me trouble, probably plant related and there aren't too many plants here! My mum suffers really badly in Australia from hayfever and she also had no trouble at all in China.
4. I must admit that the mosquitoes in Shanghai drove me crazy but if you are living in a fairly nice apartment with good screens then you should be able to limit your problems by being careful when you go outside. I found that a mosquito net on my bed kept me sane.
In short you've obviously got a less than ideal situation but I think that you can work around it. And don't be put off by #7. Of course some marriages have problems but that's true everywhere. I would say come over with your husband, give it a try. If it is too horrible return to Australia for a few months and come back when the weather is cooler.

i agree. plus, despite all the negatives listed above (and agreed to by me) - Shanghai is a pretty cool place to be - especially as an expat. Good restaurants, plenty of things to do, opportunities to travel . . .and if you have money, you can live a MORE comfortable life than one does in their native country.
What is your career in Australia? Somethign transferrable?

Thank you everyone, your responses have been immensely helpful :)
I have a lot to think about!
In regards to post 10
"1. Is your husband's job fairly generous financially? Presuming that it is then you can afford to give Shanghai a try and if it doesn't work out you can afford to return to Australia. Can you take leave from your job and then decide after you've tried Shanghai?"
Yes it is a pretty good income, not huge for Australia, but for China it would be pretty good I imagine. He's getting more than what he's getting here now, and I think apart from rent everything else would cost a lot less? generally speaking.. obviously I'm not going to go shopping at LV every day! ;)
"3. With regards to the other allergies/hayfever etc it might not be as bad as you are thinking. I get hayfever in Australia but have no problems in China...obviously it isn't pollution that causes me trouble, probably plant related and there aren't too many plants here! My mum suffers really badly in Australia from hayfever and she also had no trouble at all in China."
I know what you mean there. Actually I'm glad to have found someone else who also noticed this!! My sister and I experienced it too. In every other country we have been to we didn't have hayfever symptoms - only Australia :( That's why I didn't mention it much. I have been to China in summer (not Shanghai though) and didn't suffer from that, but at the same time suffered from asthma from the pollution and eczema from the humidity - ARGH I just can't win! :(
Yes, we were in China for 6 of the last 7 years...came back to Canada last summer.
I wonder if you could be helped by Chinese Traditional Meds? Might as well give it a go while you are over in China.
And my marriage is still damn good even tho we spent 3 years in a wee village in Botswana and all those years in China.
I think you're brave...good on ya, matey!

Hehe.. I remember corresponding with you years ago! :) before my first trip to China I think.
I have tried TCM . I've been taking it since i was a young kid, my dad makes me take it. I've tried all sorts of things.. I get so sick of trying stuff that doesn't have long term effects i just give up :(
and thanks!