Couldn't get the PWM outs on my Futaba R6208SB working properly with a Mega and v2.1 shield (read this thread about the dead zone in the middle), so I decided to try the sBUS. Thanks to remspoor, found some already working sBUS code for MWC and another post about the specifics of the sBUS serial data stream. I more-or-less just ported the MWC sBUS code to AQ - it uses 8 channels but can be programmed to use more (I don't know if the AQ code supports more than 8 channels right now?) and they're very very steady.
sBUS is an inverted serial data stream, so in order for an Arduino Mega to read it correctly, you need to pass the signal through an inverter of some kind. I used an SN74LS00N 2-input NAND that I found in a really old electronics kit, just plugged the signal into both inputs of one of the NANDs and out came a standard serial data stream.
I had already changed the LED locations on the v2.1.2 shield because I wanted to use right angle headers for the motors/RX pins, but now that sBUS works, I may remove all the RX pins, turn the motor pins around, and move the LEDs back to their proper places.
Currently, sBUS is only supported in the dev branch. Once you've downloaded the development code (beware, dev branch is not 100% free of bugs), it's as simple as uncommenting "//#define ReceiverSBUS" and "//#define SERIAL_SBUS Serial2" if you're using a Mega2560 with v2.1 shield or AQ32. It uses serial port 2 (Serial2) so it only works on boards with multiple serial ports. You can change the serial port if you like (change Serial2 to Serial3, Serial1, etc.).
UPDATE: I've now updated the sBUS library to be compatible with AQ32/Baloo boards, configurable to whatever serial port you choose. In UserConfiguration.h, there is a variable right under where you #define ReceiverSBUS that controls where the microcontroller will look for sBUS data (on AQ32 I've tested it on both Serial2 and Serial3, only Serial2 on v2.1 but it should work on other serial ports with Mega based boards). Also, I've updated it to work with up to 10 channels, so if your TX has 10 channels, feel free to comment out #define LASTCHANNEL 8 and use #define LASTCHANNEL 10! The STM32 compatibility and 10 channel capability have not been merged with the dev branch quite yet, just waiting on Kenny to clear it through and everything will be in the dev branch!