Is there a way to check whether I am connected via 802.11n vs. g or a/b ? I have gone through the Network setting of System Preferences and cannot seem to find where it would tell me what I'm using.
Network Utility (Applications/Utilities/Network Utility) will show you your link speed in the Info tab. Choose the Network Interface that you are using (probably en1). Anything over 54 MBit/s will be using N protocols
In 10.5 just hold down the 'option' key while clicking on the Airport menu bar. Note if you have G & N Macs on it will slow down to the lowest speed (depending how you set it up).
I have only G speed on my 3 year old G5, but when it is sleeping the Mac Book Pro jumps jump to N speed (my Time Capsule is set for 802.11N (b&g compatible) because of the G5 and older wireless G printer (Canon iP5200r). I am happy with this arrangement and it works well with speed considering my older devices. My Mac Book Pro gets N speed since the G5 is using it's wired connection (my setup: cable modem->D-Link 100 base 8 port router-> Time Capsule set to Bridge mode) and the Canon printer is sleeping.
Network Utility (Applications/Utilities/Network Utility) will show you your link speed in the Info tab. Choose the Network Interface that you are using (probably en1). Anything over 54 MBit/s will be using N protocols