In order to connect with a serial cable or JTAG, ( 2 different Serial type interfaces ) you will need the JTAG board.  You may not need JTAG but you most definitely will need the possibility of serial console access, if you are going to be reconfiguring interfaces for IP access.  IF your not careful you could end up disabling and interface you need to talk to the server remotely and the only way to recover it is to use the serial console access.

I am having the EXACT same problem.  When I watch the serial output while the unit boots, it will ALWAYs as in NEVER fail to reboot just after the uap0 wireless interface is instantiated.

/var/log/exim4/paniclog shows:
2009-08-08 09:34:32 socket bind() to port 25 for address 127.0.0.1 failed: Address already in use: daemon abandoned

I know the MTA is having problems but it shouldnt cause a kernel panic.

anyone have any ideas on how to fix this?

Also the unit does seem to run pretty warm compared to the Sheevaplug I have.