After sterilizing it the hydrometer was in the wort for no longer than 30 seconds or so. I usually put it in the wort because its easier for me to get a decent reading in the kettle instead of screwing around with a thief (which I end up doing anyway when sampling from carboys).
Thanks for making me feel better about the lead issue. After consulting my local homebrew shop today I was told that the hydrometer that I was using (there is a TrueBrew icon on the inner paper) has a combination lead/steel shot in the bottom that is encased with wax. So lead contamination is a non-issue in this case.
However now I've become obsessed with the concern over glass in the wort. A friend who was brewing with me mentioned that I indeed bumped the hydrometer into something post-boil. This is probably when I cracked the tip. This either happened just outside of the kettle or perhaps in my sanitizing bucket where I was keeping my chiller and other equipment.
This raises the question - when I did crack the hydrometer, did the glass simply shatter and fall to ground, or did the glass crack, stay clung to the hydrometer and fall off in the wort bucket when I took a final reading. It's hard to say. Either way, when I rack to secondary I'll wrap the end of the siphon with a (sanitized) cheese cloth or hop sack so I can get a really good filter going, and leave like two inches of beer in the bottom.