Applying for industry jobs: how early do you submit job applications? I've heard conflicting advice on this, from 6 months prior to graduation all the way to "wait until after you've graduated so you can start immediately". On the one hand you don't want to give yourself too little time to interview, but on the other I understand that employers may want you to start immediately to fill a need.  Is there anything rude/impolite/weird about applying for a job knowing that you won't be able to accept an offer for several months?  Do companies routinely wait on Ph.D.'s to finish?
Most articles found by a search for "how long does it take to find a new job" state anywhere between 3-6 months. Anecdotally, both for myself and for my friends, this is quite accurate. This, combined with the fairly frightening statistic that unemployed people have a MUCH harder time finding employment, would lead me to strongly recommend that you start well before you graduate.

Most positions that hire PhDs are familiar with the nuances of hiring someone who hasn't yet graduated. I currently work in industry, and we've had a number of people who've had to take a few days vacation to defend their thesis. You should mention during the interview process where you currently stand in your PhD work so the employer knows what to expect, but from my experience it shouldn't be too much of a problem.

Do note that some positions require the PhD of their employees, so you would not be eligible for those types of positions until you graduate. I would still recommend interviewing anyways so you're not starting from scratch... you can just contact them and continue when you actually receive the degree.