Now, I've seen women wear underwear that definitely made 'magic' happen. I tell you what, the Mormon garments do not have the same effect. The magic knickers are supposed to remind people of the covenants they've made in the temple, but they also serve as a locator to determine what is 'modest' and there for become the un-sexiest britches ever!.
If an individual is doing everything they're supposed to then the garments are both a physical and spiritual armor against evil. I think the most common Urban-Mormon Legend is of someone getting badly burned, and the burns stopped at the garments (which honestly if my face gets burned off one day, I'm not going to give a shit about my other body parts (well, save 1)). There are of course variations on that story but that's the jist of it. Everyone has an Uncle whose friend this happened to.
I think my favorite thing about the G's are the 4 S's. Showering, Swimming, Sex and Sports. The 4 times you're allowed to take off your Jesus Jammies. All wonderful justifications to whip your shirt off and show off your awesome farmer's tan!
Now I don't feel like going into the boring details about what the markings symbolize. If you wanna know go to wikipedia http://en.wikipedia.org/wiki/Temple_garment. Instead, I'm going to talk about the things that are taught about them. For example an old timer told me that the ladies garments used to have a fly. This perplexing feature raised a question, why would the lady's garments have a fly? The only reason is that 1 of the 4 S's might actually required the deed to be done with the garments on. Honestly, what was Joe thinking! Here he comes up with this great idea,"I'm gonna have me a shit load of wives!" and then he goes and takes all the fun out of having a harem. Now, don't get me wrong, a passionate jam with some clothes still on will happen from time to time but it shouldn't be the standard. Now Mormons don't teach that this was the purpose of the woman's fly, but the garment markings are symbolic, so why would they put on a useless feature? Also I don't know if that is even true. Old men like to tell stories.
Now here is my defense for the often scoffed at bulky undies. So so so many religions have sacred garments. Hasidic Jews for example. They have changed and changed the garments so that they will accommodate the LDS people's life-styles and still retain it's symbolic value. Summer garments, winter garments, military garments. I don't think it makes the religion true, but there is something comforting to know there is flexibility with some of the rules.
Honestly, I never understood why people cared so much about the 'magic underwear'. I suppose because Mormons are instructed to not show people, and keep the sacred symbols secret. But has it ever dawned on anyone that the real reason Mormon's don't show people their G's is that they are ugly as hell?!