When travelling on Qantas flights, your status is the same as if you were travelling with the staff member. IE: Your onload chances are the same, and if you purchase an upgradeable ticket (the staff member must be senior to a certain level) your chances are the same.
Where it becomes different is when travelling on other airlines. A Qantas staff member has access to a huge number of airlines, and when you are travelling with them you have the same access on many carriers. However, when travelling by yourself, you only have access to American, LAN and Finnair.
As a whole, while the staff travel process is very cheap, it can be a pain sometimes. I've spent plenty of time sitting at BNE waiting for an empty seat on a SYD flight (and it still cost me $55 - could have gone confirmed for $75). I've also had to make the 600k drive from Berlin to Frankfurt and cut my holidays short just to be able to make it home. Don't rely on it during peak periods, and especially with the recent cutbacks its becoming increasingly harder to use. Also be prepared for checkin staff to treat you like you're the scum of the earth (esp in Sydney). You just need to organise yourself well and be prepared to make changes at the last minute - which is hard if you have booked other flights, hotels etc etc.
Trips to America are good during off seasons. The BNE-LAX-BNE flight is my usual (even when I was living in Sydney) as its generally not as full. AA standby is also easy enough during off seasons and you can use QF on the LAX-JFK-LAX sector - which is always empty.
