I always flip out when I see this question. If you change your oil every 5k miles it should be ok to switch. Then the other side says if it has build up no, it will screw your engine up. Which is crap science, if its dirty clean the engine out with a higher detergent oil, which all major brands syn use. this will clean the engine out. Just use a damn good filter and change it an extra few times tell the build up is gone.

If the engine has big *** chunks of sludge. No matter what the hell you do, the engine will fail if it blocks enough oil returns to start with. If you want to know if your engine is clean pull a valve cover and you will know.