Finally got an email today saying it's been despatched (ordered back in June) and is apparently an upgraded version :-

Your RaspberryPi order has been despatched today. If you ordered a Raspberry Pi
board as part of your order we are pleased to inform you that we have sent you
the upgraded 512MB Revision 2 board to thank you for your continued patience. We
hope this upgrade is acceptable to you
Looking forward to it

Saw this on the site today - so looks like I just made the cut for getting the new boards by a single day

Will I receive the 512MB Revision 2 board?

On Monday 15th October we announced the launch of the 512MB Revision 2
Raspberry Pi board. If your order is despatched after Monday 15th October you
will automatically receive the 512MB Revision 2 board at no extra cost. If your
order was despatched before this date you will receive the 256MB Revision 1
board.