While in Africa I used an Epson P-4000 device to store photos while shooting on safari. This device was very popular with other photographers in the group, with over half of the participants having their own P-4000. With an MSRP of $699, this is not an inexpensive device.
I shoot only RAW images and I use a Canon 1DS mk II (16 mp) and a Canon 5D (12 mp). As a result, file sizes for my photos are large, averaging ~16MB.
Overall, I am not impressed with the performance of the P-4000. The P-4000 system performance was very sluggish, file navigation and opening images took way too long and made using the device inconvenient for anything other than simple file storage.
Battery performance was the worst part. I could only get about 10GB of data transferred to the P-4000 before I would run out of battery. This meant that I could only backup one cardfile before I need to recharge the P-4000. With such poor battery performance, the P-4000 cannot be your only storage source for an extended shooting trip - you are going to need to recharge it more often than you need to re-charge your camera. With that being the case, I much rather carry a laptop than a P-4000 device.
With the slow operating performance and the poor battery life, the P-4000 was relegated to a dumb storage device with nothing more than an 80GB HD for storage purposes.
Maybe the Epson does better when used with P&S digital cameras whose files are small in size and not in RAW format. But for the price, I can hardly see a casual P&S user purchasing a P-4000. As it stands, I would not recommend a P-4000 to anyone.
There is a newer Epson P-4500 available in Japan right now, it promises better battery performance and faster operation. Based on my current experience, I am not likely to give the P-4500 a chance.