I played my first game with Y-wings last night and they wiped out the opposing TIE fighters.  We played 60pts per side, with the Imperials having 4 TIEs against the 2 Y-wings. 

The Empire fielded Dark Curse, Winged Gundark and 2 Black Squadron pilots, with the Rebels having Dutch Vander(Ion Cannon and R5) and a Gray Squadron pilot(Ion Cannon, R2 astromech and proton torpedoes).  The TIEs closed fast and tried to overwhelm the Y-wings defences, but the ion cannons were worth their weight in gold.  They hit each turn, which allowed the Y-wings to stay out of the fire arc of 1/2 the TIEs each turn.  Concentrated fire killed Winged Gundark on turn 3, a Black Squadron on turn 4 and Dark Curse on turn 5(proton torpedoes as he tried to extend the range). 

End result was 3 TIEs destroyed with the last one having 1 hull point left.  Dutch Vander had 1 shield remaining while Gray squadron had taken 1 hull hit.  It was the first time either player had faced or used ion cannons, so probably a one off win, but it was fun. 

 I played a 3 Y-Wing 100-pointer the other day as a joke, and fully expected to get slaughtered.  I destroyed every single TIE Fighter and all I got was a slightly rattled Dutch Vander with Horton laughing like a maniac.

 I've been playing a 3 Y-Wing build for awhile now (Dutch, Gray & Gold) and it wins far more often than it loses. The worst matchups by far are Rebel and not Imperial. 

Jim