So as many of you know, somewhere in 2005 Subaru in its infinite wisdom decided to move the fuel filter into the tank post fuel pump. It is a metallic and plastic globe looking thing. I have read on the intarwebz everything from "It doesn't need to be changed", to "There isn't one." The Subaru workshop/maintenance manual I have gives a detail breakdown and service interval of 60k miles. Since its replacement required fuel pump removal, I had been procrastinating, but finally had it changed at 85k miles.
Wow what a difference. I had suspicions it was causing uneven boosting and fuel cut with my protune map at WOT and now all that is confirmed. Its just a happy car now. Boost is smooth and linear, I get more go with less pedal and I'm pretty certain I'll see a rather substantial uptick in MPG as I was averaging an all time low of 20-21mpg the last 5 tanks. My only regret Is I didn't change it 35k miles ago when I noticed all this stuff starting to happen.
So there you go, they are a PITA since you have to remove the rear seats, but I'd change it minimum at the 60k mile service interval, probably sooner.