they say the same thing about motor oil for automobiles. the problems really come from switching between conventional oil and synthetic, or running mixed brands at the same time. you should have no problems by switching brands, especially if you plan on sticking w/ the new brand. however, i have heard many many people swear by yamalube, and have heard it rated up there with bel-ray.
bottom line, if you want to change it, drain the tank so you're not mixing brands. other than that you shouldn't have any problems. you can switch FROM conventional TO synthetic, but the way synthetic bonds to the metal, switching back to conventional can be an issue. that being said, we have drained many motors of synthetic, filled it with conventional, changed the filter, and had 0 problems. if you're overly paranoid, you can run the conventional for a couple hundred miles in a car then change the oil again to make sure you've scrubbed most of the synthetic out of the system.
