I have bought lots of fabric from them, especially when they were a new company.
A couple of times over the last couple of years; however, I ordered fabric that showed plenty of yardage in stock: 10-20 yards, etc. Once an order is placed and paid for I assume that it is "saved" for me. Not a Fabric.com it seems. Both times I got an email a few days later w/ apologies that the fabric was no available. One time I was in the middle of a quilt for my son and needed an exact fabric, but it was gone.
This experience may be particular to me, but I seldom use them anymore.