I have been able to use nwa.com for checking in with more than 3 segments while doing mileage runs. My problem has always been getting my return boarding passes. I've only been able to print out the front end of the run and kiosks at the airport always tell me to see an agent to get boarding passes for the return trip. Once on a tight turn around in PIT the gate agent couldn't print out my boarding passes and I had to go to the front ticketing desk, back though security and almost missed the flight back to DTW. I love the look FA's give me when you get back on the plane you just got off of.