For the past 4 months since owning my 7900 I have had the cyan channel constantly throw missing lines in the nozzle check. Yesterday after running 4 cleans on the channel and a purge it didn't change. Made the call to Epson yesterday morning. They had a technician out to my place the next day (this morning). The tech checked everything out and came to the conclusion that the print head was bad. The whole process took about 4 hours. Needless to say I am very very happy with the service, and this makes me really feel good about buying an extended warranty soon.
Bonus: Epson threw in a full set of 150m Inks for the waste of purging and cleanings. So that really makes me happy!