I ordered a simple board on 8/31. I needed it fast, so I used UPS. The tracking link didn't work, so I contacted the support (their English is the typical Chinese English, worse than my German English, but I could understand it). Turns out the number they are using is not the tracking number, but you have to manually open the UPS tracking site, then search for the order number from JLCPCB with the "Track by Reference" option. After a week, the tracking page still said, that only the shipping label was printed, shipping didn't start. I asked the support again, they promised it was shipped, showing me a screenshot of some internal system, which suspiciously looks like they don't use UPS from their company site, but send the PCBs to a shipping company first, which then uses UPS, but they didn't confirm this.
After some more days they responded that UPS had a problem with my address, which was not a problem for any other company so far. I answered to the support that the address is right. After another day the support answered that the phone number was wrong (I admit that I entered "0", because I don't want that somehow it gets transferred to some telemarketer). After telling the right number, the shipment started and finally it was delivered on 9/17. The PCBs itself were flawless.
Another problem I had with some Gerber files I downloaded from a website for a FET probe (
this one). First they accepted the files, I paid by Paypal and the status said "in production". But after a day they said that the files don't have the board outlines, but e.g.
http://gerber-viewer.com has no problems to show the board. They refunded the Paypal payment and cancelled the order. They told me they don't provide just sending a fixed version of the Gerber files, I have to go through the whole order process again.
And a minor problem was with their panel service. I used this service, because according to their FAQ, this is a way to avoid the ID marking on the PCB, because it is printed on the scrap part of the panels. But I managed to order a too small panel (the single PCB was tiny), and their webpage didn't show me an error. Again I paid with Paypal and was accepted, but you guess it, then they refunded the money and cancelled the project. Just by submitting the same project again, but this time with a different number of PCBs in x/y per panel, for the same price, because it was still below 10 cm x 10 cm, it got accepted. Surely they could have fixed this on their own.
So if you have a standard board, and if you are not in a hurry (or don't use UPS, maybe I'll try this again with the right phone number), the board quality is good and one of the cheapest services. But the customer service and website etc. could be better.