There's been an interesting discussion over at Detectives Beyond Borders about how your characters talk. How do you portray accents or ethnic variations? Should you bother? Does it enhance the dialogue, or just annoy your readers? It makes interesting reading.
If you asked me to name, off the top of my frizzy head, books I could distinctly remember that used dialogue with accent, all of my responses would involve books with Scotsmen. Big, red-haired highland Scotsmen. Diana Gabaldon's Cross Stitch (Outlander in the USA) series is the one that stands out. Part of that would be because I fell in love with James Alexander Malcolm MacKenzie Fraser. Didn't everybody?
Do you need accent to portray ethnicity, or region or class? Is providing character background in the narrative, and appropriate colloquial terms enough of a clue, so the reader fills in the gaps with the voice they imagine a character to have?
How much is too much?