I'd replace it asap. It's a critical safety feature, accounting for up to 30% of your structural strength, not to mention it may be illegal in your jurisdiction to drive with a crack.
Chips are generally okay, get them filled before they spread (I had a chip 10 minutes off the lot on my cube, got it filled same day). I've also since put a hood deflector on my cube, it helps a bit, I notice more strikes on the roof, but still the odd one hits the windshield, mine is pretty heavily pitted. Don't gamble a few buck on the safety of you and your passengers.
Check this for more info:
Safety Risks With a Cracked Windshield | eHow.com http://www.aaanewsroom.net/main/Defa...&ArticleID=511