Pros:
1. Competitive prices
2. Quality definitely much better than, say, Shutterfly
Cons:
1. Production and shipping time seem longer than other companies I've used
2. Prints always arrive later than the estimated arrival date
3. Their site isn't the most user friendly.
4. BIGGEST CON: I've given Mpix 3 chances because of the quality for the price, but their packaging is awful. 2 out of the 3 times I've ordered from them, I've received photos that were bent. I would consider using them again only for small 4x6 prints for my own use. I will not use them again for larger prints or for professional prints that I provide clients.