I think i read somewhere that you can check your online status at the USCIS website before you receive the official NOA1 form, by viewing the back of the personal cheque used to pay the $170 fee. is this true? or is the application receipt number that they ask you for on the uscis site something that you can only see once the NOA1 comes?
Thanks

There will be a number that is preceeded by the letters WAC. You can use that number to check case status. There have been a rash of numbers that were incorrect on the backs of checks lately, so you never know.

yes it's true. it'll start with three letters

Your case number is on the back of the check and it is the same number that is on the NOA1 that you get in the mail. If you have the case number from the back of the check you can use that to sign up at the USCIS website. Your case number should look something like WACXXXXXXX.
Good luck