i'm joão from Portugal, Europe.
a couple of weekends ago i've updated three macs to Lion.
2009 MacMini, 2007 White Macbook, 2010 iMac 21".
problems? only with the iMac.
no connection drops but slow slow slow very slow internet. wired, speedtest marked 15Mbps download. wireless? 1Mbps, 0,3Mbps, 3Mbps, very unstable.
with Snow Leopard everything was ok.
tried every solution from every site and finally got it working flawlessly.
tried clean install instead of update.
tried new dns servers.
tried disabling ipv6.
tried remove wifi interface then add it again.
tried service order.
tried PRAM, NVRAM, SMC, you name it, reset.
tried removing preferences folder.
tried different browsers -> same symptoms.
tried disable/enable airport.
tried 10.7.1, 10.7.2, combo, delta.
tried router's firmware update.
tried putting the computer closer to the router.
tried resetting the router, factory defaults.
tried changing router's channel.
tried disabling router's firewall.
tried watch router's event log, nothing suspicious.
tried disabling router's wep password.
tried pinging a site for a couple of minutes, 2% packet loss.
tried hundreds of pages and forums...
during this attempts, macmini and macbook showed very good wireless internet speed.
iMac? slow, slow, slow, slow, slow, like seeing gmail's loading screen for more than one minute...
again and again speedtest 1Mbps, 0,3Mbps, 1Mbps, 1Mbps, 0,3Mbps, 3Mbps.
discovered the pingtest utility in the same site and iMac's ping was grade C, grade F, grade D, with big values...mac mini and macbook were alwas grade B, with low pings (imagine 25ms on them vs. 138ms on the iMac).
i was fed up with the situation, every week tried and failed. iMac's owner was wanting to get his Lion money back and stick to Snow Leopard again. imagine recent Windows switchers thinking they went back to the same situations....
but then i found this website. and then realised macbook and macmini's wi-fi were both powered by a broadcom chipset. iMac's was powered by an Atheros chipset! did what the guy says on that site (replaced Lion's Atheros kernel driver by the one on Slow Leopard), and now everything is perfect, like on Snow Leopard. very good speed.
what a relief. thank you sir.
hope it can help you.
hope it reachs apple's network developers...this is not good, you can't fail on something so simple and essential as decent wifi quality...