I notice that my copper pipe (1/2 in.) going to one of the bathrooms, has a copper strap to hold it to a stud. this is reasonable I guess (you probably don't want dissimilar metals touching each other) my question is why is the strap nailed with copper nails? any good reason?
Yes, electrolysis is the enemy of copper water lines. Dissimilar metals in contact with each other will advance corrosion, especially in a pipe that has a constant flow of water. I think that copper nails is overkill, but the original installer was doing it right! These days you can use plastic pipe supports that work pretty well.