We used the digital wallet kind (Super Digibin) and it was nice, especially when CF cards were $$$.
The batteries didn't last very long, but I got an external battery pack and it worked well. We did have 1 drive fail, but it was user replacable.
We didn't lose any data, but it was a scary thought - after that, we decided to stick with the CF cards, especially since the prices are so low now.
As for backing up data, the only concern I would have would be the fact that they are portable makes them an easy target for damage. You can get a 1TB (that's 1000 GB) Network Attached Storage for under $1000, and they have features like RAID for data security. Not nearly as easy to transport, but more secure.
The fact that I'm recovering a hard drive now may skew my answers a bit, too.

Ah well! At least it is all recoverable, and I have it backed up if it isn't.
Good luck!
Shan
Publicly declare your goals - never fear failure.
My goals:
1. Speak at the WPPI conference in 2009.
2. Be one of the top wedding photographers in the nation.
3. Get my images and articles published nationally.
4. Host my own workshops.
_______________________________
My Video Tutorials BlogVivitar WorkshopsOn 3 Galleries software for professional photographers