We have a LOC of credit account that we use for investment purposes only. Initially got it setup to access the equity in exisiting IP's we had. We use it as 20% deposits on new IP's and then get another mortgage for the balance.
You need to be very disciplined in making sure the interest is paid promptly each month.
We did get advised to split the LOC into two accounts, which gives us part we use for investment purposed and one we have for personal purposes (with just a small amount in it) in case we need it, and we don't get into any trouble with the accountant and the ATO in splitting out interest costs between investment and non-investment.
Our LOC's are with ANZ and we don't have any minimum balances and can use the account as a day to day transactional account and even have a debit card to use with it.