I use a 40 GB
Smart disk and it is great. I have 3 Gb of cards and so usually leave the Smartdisk in the hotel and dump the images into it at the end of the day. The device stores the RAW files but reads the embedded low resolution JPEG
I find it impossible to not have a look at the images and though the smallish screen is rather soft it is useful to check that there are no major problems. If used simply for storing the battery life is not too bad, Using it for viewing it is inevitably pretty short, but by sticking to using the hotel room, I only use it on the power supply.
The SmartDisk stays at home on my days out, but on holiday I would be lost without it