Search button sweetie - its been covered numerous times
http://www.350z-uk.com/forum/viewtopic.php?f=36&t=56667
Some of us wouldn't go near track without it - some of stop to read the small print and realise that it usually only covers you for impact so that means you're only covered if invovled with another car - and it is far more likely that any damage you do is going to be a result of ending up in a barrier after finding your own limits
There are individual day insurance and also companies that will give you fully comp road use and five or six track days a year as part of your cover