Ive got 3x 16gb ExtremeIII CF cards (1 in each body) and ive yet to have a problem with them...
The "all your eggs in 1 basket" is a concern, but, up until now ive not had cards fail... imo even if a card was to fail its highly likely youd be able to restore the shots already written to the card.
In my 1dmkII's, i also have 8gb SDHC extremeIII cards, giving 24gb in camera.
I think there are a few advantages of using larger cards...
- never missing a shot whilst changing cards
- with a pocketful of 2/4gb cards you could accidentally re-use one when changing, and format assuming youd forgotten to when copying the files off on your computer.
- not having to open the weathersealed door on your camera in poor conditions
- less wear and tear on the delicate CF pins/connectors in the camera body