Actually, the quality of the original iFart app is quite good - hi-res responsive interface, variety of different sounds, and it doesn't crash.
It fulfills its intentions as a gag app, and does it well.
Overall, the quality of even the borderline-useful apps is, for the most part, well above average.
I have over 950 apps installed, and use about 30 of them regularly. The majority of them are updated frequently, and are extremely helpful for particular situations which may arise.
The Zipcar app is great for locating and renting one while traveling, as is Tom-Tom, FlightTrack, Zillow Real Estate, UrbanSpoon, Yelp, Trailguru, Jaadu VNC, iCam, EyeTV, Starmap, Redlaser, when shopping, Dragon when writing, etc.
Most of the games available are extraordinary in terms of graphics, detail, and responsiveness.
Again, they do what they are intended to do, and do so extremely well - although I haven't tried all 100,000 to date, I do not find quality to be an issue with the majority of apps I have used on this platform. YMMV