I was recently searching on Youtube for a video that explains tooth grooves well.  I came across this one.  It's not a bad description, but I think it gets the whole "sealant" concept wrong.  

I almost never place a sealant any more.  I've replaced way too many of them that have a hidden (but large!) cavity underneath them.  The problem is that often the deep and bacteria-laden groove is still there.  I've told a lot of patients that they have "groovy" teeth.  Unfortunately for those who watch Brady Bunch reruns I don't mean "really cool" or "incredibly hip" when I'm referring to groovy teeth.  I mean that these deep grooves make for greater risk of cavities and other dental troubles.  

Keep checking back to www.meadfamilydental.com for more discussion about risk factors for tooth decay and what you can do about them!  It's going to be my main focus in 2011!