Comprehensively:
Withdrawing your application could take a while. You'll need to do it in writing and post it to Sheffield where it goes in another queue to be processed and then your application will be withdrawn (which again takes time) before they send them back. Plus you don't get your money back. I've confirmed this with them over the phone.
Initially I sent my application under the old Tier 1 process (Monday 23 June 2008) the day they announced the new Tier 1 scheme in Australia and it was too late to withdraw the post and all efforts to try and stop my application package from leaving Australia failed - so I had to cancel my credit card to stop them processing payment. This surprisingly worked a treat. Within 2 weeks of sending it off I got my application back (Wednesday 9 July 2008) from the UK saying that my application was rejected due to payment errors. Then within 2 days I reformated everything and submitted it under the new Tier 1 process.
There's now a 2 part process
1. Online form which you complete, print and sign and book in a biometrics scan + photograph taken
2. Another pdf form which you print and complete.
3. Pay online as well $1365 AUD as at Mid July 08 (or fill in a manual credit form and submit with your application)
Then you attend your biometrics + photograph session and then they stamp your forms.
Then you'll have to send all your forms and supporting documentation to the High Commission in Canberra.
I have heard from an agency that someone got their Tier 1 visa back in 13 days. And given that entry clearance is now no longer needed it makes the whole process much more efficient.
A friend who I am going to the UK with just got her visa approved yesterday. Her time frame was:
Submit application: 7 July 2008 via express post
Payment charged on credit card: 14 July 2008
Visa approval notice via email: 4 August 2008
So from postal sumission to approval it was approximately 20 working days. From payment processing to approval it was 3 weeks.
Personally due to my debacle above I only submitted my application
on Friday 11 July 2008 and payment was processed on 17 July 2008. So far it seems to be following the time frame that my friend experienced so I should hear something back from them next week. So excited!!!
The service standard stated on the website is that they aim to get back to you within 20 working days (4 weeks) so so far from personal experience they are sticking to it.
My other less fortunate friend who submitted her application under the old HSMP process in the first week of April 2008 still hasn't heard anything back from the UK. Even if they issue the HSMP letter she'll still have to go through entry clearance which again follows the 20 working day guideline so factor this into your time frames too.
The new process is so far proving to be much more efficient!
Hope the above information helps.