Lots of truth here.
There is no common issue from the manufacturer that leads to engine failure.
The common issue is the owners. Modifying without a tune will destroy the engine. Running Mobil 1 too long or not doing oil changes regularly on a turbocharged car will destroy the engine. Driving it like an idiot and thinking 6k RPM clutchdrops are ok will destroy the clutch and transmission.
Subarus are very reliable, and the turbo cars are no exception. They just have a lower reliability rating because people rag on them.
My WRX is an early 03, so it has the "glass" transmission. It has 130K miles on the original engine, and the original transmission. The last two and a half years I've been Rallycrossing it with a year of Stage 2 power as well. Stage 2 power *alone* is supposed to be the death of the early WRX transmissions. But this one has no issues. I did change the transmission this year, but that was for the better gearing, front LSD, and beefier design.
The engine, with 120K miles, an up-pipe leak (cheap ebay UP), and a stage 2 tune made about 225 awhp (IIRC) on IPS' dyno. That's not awesome, but it's FAR from what thrashed engine would be making.
The hardest thing about buying a WRX is finding one that has been treated well. Not babied, but taken care of.
I wouldn't say horrid. But for a small 4cyl, it's on the poor side. I average about 27-28 on the highway. My daily driving fill ups which include a lot of regular driving average around 18-19. If I drive gently and try to stay off boost, I can get about 20mpg during city driving. That's for both the Stage 2 tuned WRX, and the mostly stock power STI.
Subaru's average mileage is the one thing that disappoints me. They're going to have issues meeting minimum averages in the future now that they don't have any other car to push up into the SUV class. The Forrester and now the Outback were enlarged slightly to make them SUVs to keep the company average down.
Hopefully the Direct Injection engines they're working on will solve some of the problem.