I've seen two major problems with the rear wiper, and they both seem to be related to owner negligence.
First, especially in sloppy weather, the rear of an SUV is usually exposed to LOTS of airborne junk, such as road salt spray, dirty water, and dust. That stuff also ends up in the wiper arm, and if it's allowed to accumulate, the wiper arm can't pivot enought to provide the tension it needs to keep the blade on the glass. That arm needs to be kept clean and lubricated.
Second, and I see this all the time, some people drive around with the rear wiper running continuously. Usually, one swipe is all you need to keep the glass clean for a while, even in very rainy weather. If the wiper is left running, it ends up struggling to push a blade over dry glass, and that puts a lot of strain on the motor, even to the point of overheating it.
I had a '99 XLT, and I learned both of these things right away. Despite all of the complaints I've seen here, I never had a problem with mine.
I now have an '02 EB, and I like the wiper design MUCH better than the one on older Explorers. The wiper is mounted directly to the glass, so it doesn't need a mechanism to park the blade below the glass to allow access to the glass hatch. With a straight arm, it also does a full 180-degree wipe of the glass.