I've had the amazon.com card for at least 3 years now, and I use it for almost everything. I've had zero trouble with them, other than the one time I tried to set up the automatic payment function, and went ahead and paid the bill in case the feature wasn't operational yet. The billed amount ended up being withdrawn from my bank account twice, once from my manual payment and once from the automatic payment. THAT caused a headache...
The few times I've needed to contact customer service I've been highly pleased with the level of service received.