I change mine when I start piecing a new project and then again when I am going to start fmq.

When I hear the pop - you girls who wait til it breaks are making me cringe - it could damage your machine or worse, fly up and hit you in the eye.

I change mine often; a dull needle not only makes a little popping noise, but it can misbehave, causing stitches to skip or shredding delicate quilting thread when FMQing. If I start experiencing thread or stitching problems anytime (no matter how "new the needle), I change the needle and problems are almost always resolved.

I use titanium needles from Superior Threads - they last forever.
Bob's website says 8x longer than regular needles
Mine's been in for over a year, Oct 09 I think.
I do not sew as much as most of you, but have done 2 or 3 tops with it.

after every quilt..

I'm another that usually only changes needles when I break them. I usually sew over pins and amazingly I still don't break that many. And if I hear the machine making a 'struggling' noise, I change the needle/bobbin. Definitely makes a difference.

I have been doing more embroidery than sewing lately, but I find I don't change as often as I should on the sewing machine. If I am embroidering towels, I change after I do several and I definitely do change needles before I start doing something with less thickness. Thanks, GAgal, for the info!

The neatest article appeared in our newspaper a couple of years ago about a man in his 80s who had always wanted a sewing machine. His wife wasn't interested in sewing so after she died he bought one and began making quilts. He lived in a retirement home and they told him he couldn't sew before 6a.m. or after 10 a.m because it bothered his neighbors. He had been sewing for a couple of years and finished several quilts. His comment was that he had 'just about worn out one sewing machine needle already'!

When it breaks.

LOL!!! Happens to me all the time!!! :)