PocketMatrix

If you're talking about the CF jacket/sleave, it's a must IMHO. CF cards are cheap and you can use all kinds of stuff with the CF jacket, like modems and GPS.
The best reason to have one is the storage capacity of a CF card (128, 256 or 512MB).

I found out that datanywhere.com has them so I ordered one from them. I talked to Compaq and they sent me there.