^Yup, dead on.
If you sat under your car and turned the driveshaft 3.73 turns (think 3 turns and just under 3/4 of the fourth rotation) the back tires will fully turn once (one revolution). good to know if you ever have to figure out gears. This would be for 3.73 gears.
3.73, 4.10, etc... are all just a sort of shorthand. It's really a 3.73:1 ratio, or 4.10:1 ratio.
The steeper (higher ratio) of the gear, the quicker your car will accelerate. This is the only real benefit for them but it really is an amazing benefit. They will not add horsepower and the only real negative side effects include going through the gears faster because of the higher RPMs and your gas mileage may also be affected by 1 or 2 MPGs. Some drivers have reported an increase by this much though as well.
As a rule of thumb manual transmissions will upgrade to the 3.73 while automatics will go for the higher 4.10 but it's up to personal preference on which ratio to choose, and there are plenty of other options out there too.
