I haven't had very much experience with centres/resellers as I've usually bought online. When my parents bought an iMac, they got it from Next Byte in Geelong. Service was reasonable, but they didn't throw anything extra in.
I live near the Moonee Ponds Apple Centre so I've stopped by there a few times, again pretty helpful, but as soon as I enquired about buying an iPod they started "highly recommending" all sort of accessories.
My uncle bought an iMac on Saturday (I'm slowly converting the family

) at Dicksmith Powerhouse, of all places, and the special Apple guy there was particularly helpful. They had a special offer running - buy Applecare with your product and get either MS Office or a 2GB Nano for free. He also took $40 off a Wireless modem router, which I was quite impressed with.
I've also stopped by the centre on Elizabeth street from time to time. The service staff seem a little useless to be honest. I hear them telling customer that if they want to run Windows they'll need 2GB of RAM and other such nonsense.
So the moral of the story is, it probably doesn't really matter where you buy it as they're pretty tight across the board (well except for Dick Smith). The good thing is, even if you order online you can still take it in anywhere and AppleCare will cover it.