American now has Wifi access on select planes, including 747 and MD-80's. Fees are $9.95 US for an all day pass and are currently running a free promotion for first time users.
The free promo requires registering an account using only an email address and code which they provide, no credit card is required. This means you can probably sign up using multiple email accounts and username for as long as the promo lasts.
When you sign up it assures you that the system is very secure and tested thoroughly by the FAA, the captive portal authentication is SSL based but after authenticating you are still vulnerable to any standard wireless man in the middle attack as there is no WEP, WPA or VPN protection.
Setting my radio to monitor mode quickly showed everyone's traffic on the flight, so security is non-existent at best.
Speeds were very good, similar to DSL connection but lots of intermittent latency made video streaming from Hulu unwatchable.
Here is a screen grab of an in-flight speed test.
