This course I am building has grown to 120 Megs and I am just 75% done. Every slide has a relevant background image (I am buying them from Canstock.com, medium and large JPEG). So, Storyline slowed to a crawl at about slide 35. I took to switching off the BG JPEG and no more freezes and lockups. Likely this has been commented on before but thought it worth mentioning.