Op/ED's are a very nice way to learn about new songs, artists, and bands from Japan. Unlike in America where all of our television and cartoons have theme songs written by out of work musicians, Japan actually uses top selling artists, and almost every song released in an anime hits the top of the music charts. For me, seeing translations to lyrics in the animes is really not needed, as most Japanese songs don't make a whole lot of sense anyways, but I always enjoy easy to read romaji with the song so I can sing along with it. If I can't sing along with it then I usually just skip it.
OP's can really help set a mood for the anime if you do it correctly. If it's really fun and upbeat then it can build some excitement for the rest of the show. Likewise if it's really sad and somber then it can put your mind into a sad mood to prepare for what's to come. Endings are a little less useful, but when done correctly they can really continue the mood of the show and leave on a high/low note. Particularly notable was the ending for Gunslinger girl: Il Teatrino (Lia - Doll). The show actually flowed directly into the ED and used the song's beginning as a sort of soundtrack for the end of each episode. Those who have seen/heard this will know exactly what I'm talking about. A great OP was Pre-Parade for Toradora because it was really upbeat with an attitude that seemed to fit the show style and even Taiga's personality perfectly, so it really brought a little extra sparkle to the beginnings of the show.