You got some great feedback on this already, but I'll throw in some new stuff that I hope helps you.
1) As a rule of thumb, if your bees aren't consuming at least a gallon of sugar syrup each week, you shouldn't be supplementing them. When there is a need for syrup, the bees will often consume a gallon per day!
2) Make sure you're using the right sugar/water ratio for your particular syrup application. See http://www.beecare.com/Feeding/Syrup/Syrup.htm
for more detail on this.
3) Keeping syrup on the hive too long not only discourages foraging (which produces better honey than syrup), but it also attracts external pests, such as ants, wax moths, beetles, etc.
4) If you have a need to quickly encourage feeding via a hive-top feeder of some kind, consider using a proven feeding stimulant such as Honey-B-Healthy. It not only increases the rate of consumption, but does other things for your bees. See http://www.beecare.com/DiseasesMedications/Honey-B-Healthy.htm
for more information.