It doesn't leave any sticky residue and can be written on with a Sharpie very easily. I use it to keep track of the differences between Archer and Lyla. It not only serves as a helpful visual reminder to me, but also to Adam, our moms and anyone else we've managed to convince to help us out. I can make the blanket statement: "Anything with green tape is for Lyla and anything with blue tape is for Archer."
I use it to label their car seats. Since Archer is bigger than Lyla, the straps are in different positions on his car seat than on hers. I just wrapped part of the handle with tape corresponding to each of their car seats.
They also each use different diaper cream. So I stuck some tape around the bottom of each tube to designate who gets what. Archer does well with A&D. Since Lyla has switched to formula her poop has been more irritating to her. Our pediatrician recommended using Calmoseptine with every diaper change and it has cleared up her little bottom. So the tape helps whoever is changing diapers know what to use on each baby.
Finally, I use the tape to label each baby's bottles. We used to have the same bottles for each baby, so it was a little more confusing when grabbing a bottle from the fridge. We switched to a different kind for Lyla after trying out a sample. Archer likes the Dr. Brown's bottles (and the millions of parts that go with each one) while Lyla does better with the Avent bottles. When we would wake up in the middle of the night to grab a bottle, it was helpful to just look for the correct tape color when the bottles were the same. I still use the tape on the bottles even though we use different bottles for each baby. Since Lyla has a dairy allergy, I don't want anyone to make the mistake of giving her Archer's breast milk.
Who knew tape could be so handy?!