Very little. The highest concentration of THC is in the female plant and the males will usually turn the females into males. So anything left unattended will have a very low THC count.
Different kinds of strains of marijuana have different THC levels. Although, THC levels today are a lot higher than they were in the 60's and 70's. People really know what there doing now, and are...
Contrary to popular belief, there is absolutely no THC in the black tar that builds up on your pipe/bong/etc.
The reason you get high is due to oxygen deprivation.
Except for the resin you scrape...
I don't believe there is such thing as "too much" marijuana... however, due to the variance in amounts of THC in each "bud" of marijuana it is impossible to determine how much is "too much". Any...
THC is a compound that occurs naturally in Marijuana. However, through breeding and other growing methods, it is possible to change the amount of THC in the plant.