For old symbol firmware (symbol b radios) and cisco G radios use the "speed ofdm separate" option on the dot11 interface otherwise the handheld will never send at the 11mb rate. [ Symbol tech support might ask you to disable rates 6 and 9 to solve the same problem but I prefer this solution ]

If you are using WPA the symbol firmware doesn't update the keys correctly on the first few packets after roaming so disable the holdtime using

"countermeasure tkip holdtime 0", again on the dot11 interface.

Cisco AP's seems to perform better when you set the unknown device activity timeout to 1800 seconds (instead of the default 60 seconds)

Let me know if you have any issues. I have 160 or so MC9000 class devices spread across 113 retail stores using 802.1x PEAP authentication to a MS IAS server. It's been in production for a couple of years.