I agree with Ironlord, it's more acceptable in the earlier pieces. I always mention it if I find any because certain eBayers, and especially collectors, can be super picky about flaws, whether natural or acquired. I've had glassware returned for a bubble on the inside bottom of a non-translucent piece that you'd practically need a microscope to see. It's a small percentage of people in my experience that make these kinds of returns, but it's extremely annoying nonetheless and has caused me to rewrite my disclaimers about antique & vintage items umpteen times. Sometimes I want to say, "if you spent that $ at Wal-Mart for a packaged jewelry box made in China, or at Big Lots for a mass-produced vase, do you think it would be flawless? So why do you expect a decades-old delicate pottery piece to be? And which one do you think will fall apart faster?"
Crazing is different from cracks; crazing is to the glaze itself and caused by stressors (age, temperature changes, a variety of things) that the glaze can't handle. It doesn't affect the piece's ability to support a load, whereas cracks do. It is usally uniform throughout the piece and not just in one place. There is more good info on wikipedia about crazing:
http://en.wikipedia.org/wiki/CrazingJust try to disclose that there is crazing if you find it and are selling the piece(s).