I need the advice from those who have done the up grade from Leopard to Snow Leopard and then to Lion. I have a Mac Pro running an up-to-date Leopard even though I have a disk to up grade to Snow Leopard I never did it just because the system worked just fine. The reason I would like to do it now is to gain access to the iCloud to use with my other Apple products. My hesitation is that I have multiple programs that I use for daily use and they would be very expensive to up grade just to use the iCloud. These are mostly related to photography like CS4, Portrait Professional, Lightroom, ColorMunki, and an HP Photo Printer that they no longer make the Photosmart B8850. Can anyone enlighten me as to what problems I will have if I up grade my OS?