Every 6 months, I get a slew of auto insurance quotes. Most auto insurance is sold in 6-month terms. I would say that on average, we stay with a company for one year. We're currently with Allstate, who offers free quotes here. They've gotten us for one year now, which is good. They actually raised our rates for no reason since out last term, but I failed to find a better deal so I begrudgingly stuck with them. It's still a good rate.
In the 12 or so years that I have been driving, I have been insured by Geico, 21st Century, Nationwide, Progressive (twice) and now Allstate. I look at auto insurance renewal time as a shopping experience. Unfortunately some people just look at it as another renewal and fork over a check. Don't do that!
It's YOUR money, so act like it! Just like you're going to shop around for your new TV or a new computer, shop around for insurance. Think of the internet as your store and go get some quotes. I have switched insurance companies 5 times and have probably saved hundreds of dollars because I don't settle for the rate that my existing company wants to give me. What about loyalty? Screw loyalty! If companies want loyalty, they'd better earn it by charging competitive prices!
One important thing to remember is to not let your insurance lapse. Make sure you're having your new company start your insurance on the day your old one is dropping you.
Dropping one insurance carrier and picking up another is quite easy. Most major carriers now offer free (and usually quick) online insurance quotes. So get out there and get some dang quotes!