I think it depends on your route. I just got back from a trip where I helped 2 friends book their flights with miles. One friend booked a simple round trip online with no issues. The other friend had a 23 hour transfer which we couldn't get the system to recognize in addition to a future domestic stopover/one way (ORD-MUC 23 hr transfer, MUC-AMS, 5 days, AMS-ORD, 6 months, ORD-ABQ), so he had to call in. The agent understood the challenge online and booked the award ticket, and waived the agent fee since he couldn't book it online.