I've watched lots of foreign films. I've seen lots of bad dubbing. But I've also seen lots of bad subbing - subtitles that were incomplete or poorly translated, requiring me to back up several times in the movie and read the text over and over (ignoring what's actually happening on the screen) in an attempt to figure out what the characters are talking about.
So dubbing's better, right?
Not necessarily. Dubbing has its own problems, and they have been thoroughly described above.
So which is better? One's better than the other, right? Right? TELL ME WHAT TO THINK!
Please. Both have their merits, and I tend to watch most movies both ways (hooray for DVD). But dubbing is not the Pit of Evil and Despair the above writeups tend to make it out to be. Cowboy Bebop, for instance, is proof that dubs can be just as good (and maybe even a little bit better) than their subtitled counterparts. The translation is excellent, all the voice actors - even for bit parts like Rocco Bonarro - are fantastic, and great care was taken to make the speech match the mouth movements of the characters.
I also recently watched Jet Li's Fist of Legend on DVD. While I was disappointed that there was no subtitled version, the dubbing was fine - the translation was clear, lip movements matched well, and voices were well chosen. The voice actor for Jet Li actually sounded like Li. It didn't detract from the movie at all.
So both dubbing and subbing can be done poorly or well. I don't think either one has an inherent, innate advantage over the other.