I disagree with most of whats been said here.

Synthetic oil permeates the walls of the cylinder to provide supirior lubrication over dino juice. If you go back to standard oil after using synthetic, the smaller molecules in standard oil will literally slip by the rings because the synthetic oil has already become embedded in the cylinder wall. There is a good chance it will cause your engine to burn oil and smoke like crazy.

Its easy to yes you can switch back and fourth, because I can also switch from 93 octane to 89 in my car all the time.. but i dont because 93 octance isnt nececary and swithing back and fourth is just stupid.

Its your decision, but if you ask me I say no for the above reasons i stated and the fact that synthetic is worth every penny... do the math on cost VS frequency of oil change, and then factor in how synthetic is better for the life and performance of your engine.

 

The reason some cars leak after using sythetic is because it has a tendancy to 'run' easier. That is so that when the oil is flying around inside your enigine, it runs back down into the oil pan when its done. However this running effect has caused some aftermarket companies to disallow the use of synthetic oils on some valvetrain products i.e. comp camshafts. So make sure you check if you have any serious aftermarket products in your engine. Synthetic oil is definately better and recommended by many. If you use it you can also afford to double your oil-change intervals because it does not break down under heat as easily as normal oil. That is why we use synthetic oil here at work on our jet and turboprop engines. That should offset the cost of the oil and shouldnt hurt your car at all. Infact that was one of the selling points of Mobil 1 when they first introduced synthetic oil.