Another somewhat stuck expat here.
I'd say don't do it.
My DH is Aussie so it was always a given that we were likely to move here, especially as he's very close to his mum and didn't want to leave her on her own. My dad lives near my sister, so I wasn't quite leaving him on his own in the same way.
We've been her 9 years now and I'm still homesick - but that's because we go back every year so my boys can see my Dad and other family and friends. We're lucky to be able to afford to do that, and that's largely because we don't have to pay rent on a house. We're in NSW, semi-rural.
Rent is vicious out here, as are house prices - we're near the motorway to Sydney though, so that probably pushes local prices up.
Food is generally more expensive, as are cars, clothes, and most things except petrol. DOn't get me started on the full price of books!
Although there are discount places to go where you can get them more reasonably priced, or even online places like Book Depository.
School system - well I don't know about the other states, but I do know that in NSW you go to the school in whose catchment you live. It is possible to apply to go to a different school, but you will be refused if the other school is near their number limit, or in their "buffer zone" (they must keep 2 spaces free per class for children who move into the catchment area). In my experience so far of the school, the community is much more fluid than in the UK (although it might be more fluid there now too) - so there is a fair amount of people leaving and new ones arriving through the year. Might just be our area though.
If your catchment school is good, that's all fine because you WILL have a place there, they have to take your child. But if it's shit, then you're stuck with it unless you can get a place in an out-of-catchment area school, which is much harder than it used to be.
The Hague convention will kick in after a certain period of time, I think it's 6 months, but I could be wrong. After that, your children are said to be in "regular residence" (I think that's the phrase) in Australia and you won't be able to remove them back to the UK without your DH's permission. There are a number of people I've met over here who have come over with the husbands, either British or Australian husbands, who have then broken up with them and been stuck here, as Iborgia (and some others) said.
Make no mistake, it's a LOT of pressure moving here - you have to adjust to the new place, the new people, new laws, finding your way around the different systems and ALL of this without any family back-up. I was lucky - I had MIL but also I had a 20mo baby, so I went out and found playgroups and made friends that way. It can be quite hard to do without a job though.
The weather - ah, the weather. If you're a sun and heat fan, then yes, this is a great place! If you're not, not so much. I'm not. I hate the summer. It's too fecking hot, I can't move without sweating, I hate it. I can't go outside for most of it except for short trips. Dreams of beach-front houses - these are the most expensive and the least likely that you will be able to access. There are a lot of coastal towns, of course, and the beaches are generally better than the UK too - but when it's really hot, it's a bit much.
Cockroaches - everywhere. Big ones. We have an old house though so it's harder to keep the feckers out. Spiders don't bother us, but the roaches...
Culture - wouldn't worry about it unless you're desperate to be going to a different stage play every week, or new high brow art museum or fashion show, or something. There's plenty of culture here - it might not be the same, but it's here. Some things aren't so different from the UK - some things are similar but not quite the same, and some things are very different.
But I would say the hardest bit is being so fucking far away from family and lifelong friends all the time, and knowing that if there was any kind of crisis, the chance of me getting home in time is very low. 9 years down the track, that still cuts me - more now, in fact, as my Dad gets older and older. Skype helps but it's not the same. Bring on the teleport machine! But until then, my advice to you is to say No.