I have cards with factory Tantalum capacitors that have exploded.

Example:

http://picasaweb.google.com/teozenios/NubusCards#5067908435668848786 (lower right side)

http://en.wikipedia.org/wiki/Tantalum_capacitor

"Self-destruction and thermal runawayTantalum capacitors are under some conditions prone to self-destruction by thermal runaway. The capacitor typically consists of a sintered tantalum sponge acting as the anode, a manganese dioxide cathode, and a dielectric layer of tantalum pentoxide created on the tantalum sponge surface by anodizing. The tantalum oxide layer may have weak spots that undergo dielectric breakdown during a voltage spike. The tantalum then comes to direct contact with manganese dioxide and the leakage current causes a local heating; a chemical reaction then produces manganese(III) oxide and regenerates (self-heals) the tantalum oxide layer.

If the energy dissipated at the failure point is high enough, a self-sustaining exothermic reaction may occur, similar to the thermite reaction, with tantalum as fuel and manganese dioxide as oxidizer, destroying the capacitor and occasionally producing smoke and possibly flame.[3]"

And you don't have to have much over voltage to have issues.