Valentine's Days specific origins are not known, but what is known is that you are in big trouble if you forget that the 14th of February is Valentine's Day and you have a special partner!
Make sure you mark Saint Valentine's special day in your calendar, personal organiser etc, otherwise, you could be up for a lot of begging and grovelling to gain back the favour of your loved one.
As with most special days, commercialism has taken over and Valentine's Day is a huge money spinner for florists and other love related shops. Remember though, that a little thought can often go a lot further than a spending lots of money. Spending a lot of money on your partner has been known to work though ;)
Some couples that don't want to deal with the hectic day itself agree to spend time together on a different day instead. Then you aren't competing for restaurant bookings etc and can have a nice relaxing, romantic night you plan between yourselves.
Remember, just make sure you do something for your Valentine!