Can no longer edit my contacts in iOS 5
This seems to be a bug. I ran into this same problem over the weekend when I was trying to add a new contact I had received over SMS. It seems that depending on how you get to the contact screen, the "Done" button may not be there. If you open the Contacts app (instead of getting to your contacts from the Phone app), you should get a contact screen that has the save button. Hope this helps.