So far I've had one order from - bought some silver PLA and a roll of Kapton tape. When I realized I had mistakenly ordered 1.75mm filament instead of 3mm, ProtoParadigm offered to send me the correct filament before even receiving the wrong one back! (As it happened, the silver in 3mm was backordered, so it took a while to get it, but it still came in long before my PB did!)
I was very happy with the products and the service, and will order again. Their blog contains a lot of useful information as well.