Given the date of GM, I'd be really surprised if Apple could get 10.5 out in October.
Apple will only offer OSX10.5 free upgrades AFTER Apple THEMSELVES have announced 10.5. Since they haven't, if you buy an Apple machine today you'll still have to pay full price for 10.5 when it comes out.
I was at an Apple Store on Saturday. Lots of people asking the same quesion but I asked three different floor staff if a free Leopard upgrade was due if I bought a 24" iMac that day. One said 'probably not, although keep checking apple.com', one said 'I couldn't possibly comment because I just don't know' and the third was along the lines of 'chances are you probably will, but don't hold me to account on that'. I'm waiting until the 26th...