Synthetic oil won't break down as quickly as conventional oil, gives better protection and longer life. I've seen people with synthetic oil loose their coolant, drive the car till it stops, tow it in, fix the coolant leak, replace coolant, do an oil change, start the car up and drive it for years with no problems. I also have a few trucks used for snow plowing that I used to run 20w50 conventional oil in and because the trucks runs hot while working. I used to have a loss of oil pressure around 230-250 degrees. I switched to 5w50 synthetic and the oil pressure stays up now even when hot. Excellent product, I run it in all the vehicles now but still change it at 5000 kilometer or 3 months. Strongly suggested for those out there who forget to do their oil changes regularly or courier/ work vehicles.
Heres the link to an explaination from Castrol http://www.castrol.com/castrol/genericarticle.do?categoryId=8264018&contentId=6003233