OK, I've now been through and filled almost every pin on the Samtec 
connector for Balloon 3. You can see it at

http://www.martin-jones.com/balloon/samtec-pinout.pdf

The changes from Balloon 2 are:
- VDD_3V is now VDD_IO (still a 3.3V supply)
- VDD_5V is now VDD_RAW (which is 'rough' 5V)
- MBREQ/DREQ<0> and MBGNT/DVAL<0> are present on the Samtec so 
motherboard devices can do bus mastering and DMA
- SDCLK0 and the 48MHz clock are available because they're probably useful
- The complete 10-bit camera interface is available, some of which 
handily doubles as a synchronous serial port
- all 3 serial ports are available. COM1 is now the Bluetooth serial 
port, COM2 is the Full-featured UART, and COM3 is the Standard/IrDA 
UART. The handshake lines (CTS and RTS) for COM1 are available (in 
rather illogical places) but not for the Full-featured UART. There just 
isn't room.
- All LCD lines available including the new ones (LCD_D16, LCD_D17, 
L_VSYNC and L_CS) for displays with their own framebuffers
- USB slave is there, and USB host, and pins for either a second USB 
host or USB OTG
- I2S or AC97 audio is available on the same pins as Balloon 2 with a 
couple of extra ones for the extra AC97 signals
- analogue audio input is now line level rather than mic level.
- MMC is crammed in to some remaining spare pins

The biggest issue has been to map GPIO functions from Balloon 2 on to 
Balloon 3. My policy has been to map them to their nearest equivalent 
function, which is OK most of the time, and if there is a new function, 
to map it to a pin nobody's told me they're using, and make sure that 
any general-purpose IO pins can still be used as such even if it 
involves turning off a peripheral (normally MMC). The notable oddities are:
pin 148, NAND_SM_CF_OFF is now RUN_NAND (may be opposite sense)
pin 162, FLASH_RDY is now BT_RTS (FLASH_RDY didn't seem to do anything 
anyway)
pin 166, uncommitted GP12, is now MMCLK
pin 168, SSID_ID, is now MMCMD
pin 170, USB_IRQ, is now GPIO1 (also used as an interrupt)
pin 186, NEG_LCD_RUN, is now RUN_LCD_BACKLIGHT
pin 190, RTC_NINT, is now L_VSYNC
pin 192, USB_OFF, is now L_CS
pin 194, uncommitted GP26, is now MMDAT<0>
pin 196, AUDIO_OFF, is now MMDAT<1>
Other bits and pieces have gone on previously unused pins.

If you have problems with any of this, or I've committed any EMC or 
layout howlers, please shout now.

Cheers
Chris

-- 
Chris Jones - chris@martin-jones.com
Martin-Jones Technology Ltd, makers of Solidlights
http://www.solidlights.co.uk/