It is a simple item which is a Secure Drive to Compact Flash converter commonly called SD/CF converter. The unit has the same size that a IBM Microdrive or CompactFlash II model.
Why this unit is so convenient ? Firstly, the CF memory is well know (from the beginning) as capacity limited, as speed transfer limited and mainly for me as an expensive memory card comparing to the SD. Today, we can see that the SD technology and price are grow faster in terms of speed and price goes down.
Secondly, I always bring along my laptop with me wherever in holiday. My little laptop has a build-in SD reader. It is just nice to extract rapidly every pictures.
My configuration is one SD/CF converter with 2 SD of 8Gb Ultra III and a bunch of old 1Gb SD from my old point and shoot camera as pares.
I touch wood. I am never been out of memory card for any photo session including the wedding one ;)
For whom who are interested to this solution, there is plenty of converter available on the famous auction website for about $15. Beware of choosing a SDHC model if you intend to use more that 2Gb SD cards.