So if I {cloudshift} a creature, it comes back into play with summoning sickness because it's considered a "new" creature correct? Or also, if I cloudshift {Geralf's Messanger}, and his undying's activated, he comes back into play tapped and loses the +1/+1 counters? Any help would be appreciated.
Yes to both. Anything that is removed from the battlefield and then put back to the battlefield is treated as though it just entered for the first time.
Also, please use the curly brackets around cards to link them. I modified your post with them, so quote it to see what I mean if you don't know. It helps keep things nice and easy for people to look up!