The only thing I know about Fall Out Boy and My Chemical Romance is that they are popular with white teenage girls. If I didn't work in a high school, I'd never hear of them. I've heard 30-second clips on ITunes, out of curiosity, and they just seem to be another fun pop-rock band. Certainly not something I'd hate because they are so easy to avoid, unless your radio dial is broken.
The band whose popularity I don't understand to this day is U2. I've always thought that they were musically weak. The songs that they've put out over the past 20+ years are some of the most boring, adult-contemporary, safe and radio-friendly pap out there, perfect for selling commercial products or relaxing patients in a dentist's office. That's not the worst part though, as lots of bands fit this definition. The worst part is that they think that they are changing the world in some way. It seems like they want to be on the same level as say, the Clash or Bob Dylan. If the lead singer didn't act like the biggest, most pious, egomaniac retard, I would give these guys a pardon on the fact that they've raised some dough for Africa. But Christ, I wish that they would give it a break already.