Wow, that's a loaded question!

They can be used safely but always have the potential for danger...especially when charging them.

I use dedicated Lithium chargers like the Kokam LIPO-402 charger that requires the user to set voltage and current levels via jumpers.

Charging the pack in a pyrex (glass) or similar container helps safety.

The new Kokam "Safety Guard" helps safety.

So far, nothing really eliminates the hazzard potential but mearly reduces it.