the only time I write "ain't" is to make a point, and obviously I'd never have used that word in court when I was practicing, but I use it in casual conversation all the time, as do my peers.
Ack! I despise that word. 'ain't'. Might as well scrape your fingernails across the chalkboard.

It always makes me think the people speaking it are trashy school drop-outs. (not saying you all are whoever says it, just makes my flesh crawl. )