I've recently received notes from two editors on two different pieces. And the gist of both was: tighten your dialog.
I've always thought my dialog was particularly scintillating. Also, lately, I've gotten it into my head that if a character (other than the POV character) has a big idea to present, it's best to do it as an extended dialog so that the character can use his or her own voice. Turns out that's not true. In literature as in life, lots of talking can be boring. In order to make the talk sound realistic, the writer might also start throwing in lots of "wells" and "you knows" and "really?s"--which go unnoticed in speech but really clutter up the written page.
What's the solution? Paraphrase. As a former academic, I still shudder at the word. You want the unfiltered voice whenever possible, right? But in this case, you paraphrase through the perception of either the interlocutor, or the overall narrator, if the later has a distinctive voice. You don't just paraphrase neutrally, relaying what the speaker is saying like some objective reporter. You say what the other person actually hears, and thinks about what he or she's hearing, which will be colored by their personality and prejudices. The filter doesn't fuzz things up, but adds information and nuance. You can then spice up the dialog with brief, actual quotes from both speakers, just to give the flavor their individual voices.
Obviously this isn't an issue for short dialogs, or for fiction in which dialog plays an unusually important structural role. But I myself have been annoyed by page after page of dialog in fiction--especially if I sense that the dialog is actually just exposition that the author can't think of another way to bring out. And I especially don't like it when the speaker pauses just so the other character can say "really?"--which is a lame way to break up long paragraphs. I am looking through my own work now for those "really?s" and "tell me mores," so I can replace them with something revealing about the character saying them. If the character truly has nothing more to say than "really?" then he should remain silent. The presence of "really?," more often than not, means the speaker is going on too long, and it's probably time for another paraphrase.