ScotsSal

I think it's just an employer's preference not to have too much of the visa's time 'wasted' as I think it is valid from the date it is approved (not sure if you can apply for a later vaildity date), so by getting one approved in October and you don't want to start work until January, you are essentially 'wasting' 4mths of their sponsorship that they are paying for.

I got my 457 visa approved in less than 2wks once I managed to get my chest x-ray done. The company will not normally book your flights until the visa is approved. Most may not arrange the shipment of your belongings until then either. Luckily, I managed to get mine packed up and stored before the visa approval, but it was only because it was less than a container so needed to be stored anyway, until other small shipments were matched up with it to make a full container. They wouldn't ship it out of the UK until the visa was approved, though. My visa was valid from 20th July 2011, but due to flight availability, I didn't arrive in Perth until 5th August.

Pollyana

You can do it and many people on here have. You can advise your CO that you intend to visit Australia to get a feel of where to live etc, have a look round - its just a holiday. You also need to be aware that if the 457 is not granted for some reason before the tourist visa is due to expire then you have to leave - so selling houses etc in advance is not always a good idea - but if you abide by the rules of each visa its perfectly legal. One is for a holiday with the intention of leaving again, the other is for the job. The tourist visa shouldn't be used as one on which to "come to Australia and wait for the 457 grant", it should be used for a holiday

Having had a friend in this situation I've also discussed it with an agent and yes it is do-able.