My MBP, MB's, and an older PB all connect with Leopard just fine. Routers include AEBS 802.11n, ABS 802.11g, Airport Express, and an old Belkin 802.11b. I am in a single family home, with no neighbors too close. Most of the time, I can't see any other networks...
I have 2.4Ghz cordless phones and a microwave within 15ft of my AEBS, and no real issues.
My AEBS connection speed shows 130Mbs pretty much all the time.
My MB (802.11g) with an ABS 802.11g shows 54Mbs most of the time, but does drop down to a lower speed ocassionally when the cordless phones are in use - but it does not drop connections.
None of the machines drop connections, but ocassionally will have airport turned off after sleep - but this is vary rare.
I have played around with Interface Robustness (?) a few times, but I think it is turned off on all of my routers and Mac's.
I run Video iChats every day for several hours (sometimes all day), and the wireless connections stay connected the whole time.
Not sure what other settings to give you...
It seems like some machines just have Airport issues. I am not sure if it is a Router issue, or something on the Mac, or something else.
My MBP is a C2D 2.33 with 802.11n
My MB is a CD 2.0 with 802.11g
My PB is a Titanium 1.0 with 802.11b.
I have an Apple TV with 802.11n also.
All of my machines were originally loaded with Tiger and then upgraded in place (no archive and install) with Leopard. All machines have 10.5.2 with all security update also.
Maybe there is some environmental issue here. Have you tried taking your Mac to another location to see if it is any better? Say to a friends house, or to a coffee shop, etc?
I know alot of people seem to have issues, but for alot of us, everything seems to be working fine...
Now the Airport Disk on the AEBS is another story all together...
