Sacolton,
They keep meticulous records on tithing donations. Around christmastime they have "Tithing settlement" where they grill you on whether you have truly contributed 10% of your income. This is in addition to Fast Offering, missionary donations etc.
Yes there is magic underwear. It used to be angle/wrist length, but has undergone several iterations. Truly hideous to behold. Different things have been taught about proper garment usage. Some leaders have taught that it should be worn at all times, briefly/partially exposing the body during showers. Some have advocated wearing them even during sex. In recent years, there has been less emphasis on this rigid interpretation. People nowadays are genrally counseled to remove them during sex or sports.
Funny thing is, garments are supposed to be a shield and protection not only against sin, but from physical harm. Faith promoting stories abound. But for some strange reason, the Mormon God doesn't want children to be protected by wearing garments (you get your garments after the washing and annointing ceremony)