find my iphone/iphone4/cloud set up

hello. if i used my apple id to set up find my iphone on my iphone 4 when i bought it and that is the same apple id i use for itunes and for registering products and even logging into this board will i have a problem updating my phone and starting icloud? i saw where some people were getting an error of 'that email is already in use' or something like that. i'm wary of updating because of this. thanks for any help.