Vowel Cry wrote:
Do video cards usually degrade over time or is it usually all at
once?


One failure mechanism, is described here.

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

"In modern consumer electronic devices, ICs rarely fail due to
electromigration effects. This is because proper semiconductor
design practices incorporate the effects of electromigration
into the IC's layout."

Mostly true, except when it's not true :-)

Especially when you're building a GPU with three billion transistor
equivalents. The temptation to make the wires too thin, is
overpowering :-)

Paul