I bought my EF100-400L new in Jun 2010. I just fedex'd it to canon this morning for a suspected bad IS motor. It was doing the 2-3 times a sec jumping thing mentioned above. Never been dropped, no scratches or marks on the body, no "rough" handling, etc. Ironically the problem is worse when IS and AF are switched to "off". I will post the repair cost when canon evaluates the lens. I have 3 other canon lenses with IS (EFS 17-85, 24-105L & 70-300), all owned longer than the 100-400L, and none of them have had a problem with IS (yet).