I've used DiskFaktory for a couple projects, and a few subsequent re-pressings. They do good work, IMO. I can't say they are great about keeping you in the loop as to the status of your order (if things get held up or something). They have an online order status page you can check, which is OK.
On our last project I had them do, there was a database error and they lost a bunch of orders. The ONLY way they knew of our order was because I called them to check status, as our order status page had sat at the same place for like 2 weeks.
So it took us longer to get our CD's, and they didn't seem to care that we had paid for rush processing and shipping, etc. Still charged us for all the rushed stuff, and we got the CD's 2 weeks later than we were supposed to. I called and complained and got a discount on future orders, which worked out because we've had to re-order like 4 times.
I've never used their mastering services.
We've done both duplicating and replicating. Both products were of great quality.