The question of whether or not Synthetic motor oils should be used is one that is asked on a regular basis (I have asked it myself in one way or another). I came across a web site that seems to answer a lot of the usual concerns in a seemingly objective and technical way. The issues of mixing mineral oils with Synthetic oils, leaking seals, or changing from one style to another are all discussed and explained. I found it an interesting read and hope that some of you may also get some value from it. Car Bibles : The Engine Oil Bible
I can't vouch for the accuracy of the information on the site, so make your own assessment before using it.