Upgrading to iCloud in an iPhone 4s that has ios5

I bought for myself an Iphone 4s that has ios5. Snow leopard works fine for me and I’m happy about that, but upgrading to iCloud would be the best thing to do. I’m thinking of upgrading to iCloud, but I just have some concern that doing so would cause disruptions of major kind. Just to be sure, I have backed up my drive. Please note that I’ve been using mail of Mac and that it is of paramount importance that lr3 and cs5 would not be affected. Please share any experience you have in upgrading to iCloud so I wouldn’t think twice of doing it.
