God yes! Really this feature is a no-brainer & should have been looked at by now.
Yes, manually sorting using the arrows is nice, but what happens when you have a big gallery & the photo you want to move is at the end & you want it towards the beginning?? Try it out & see. Basically, since you can't keep moving the photo forward to the end & have it come out at the beginning (which would make sense), you have to *click click click* going backwards until you get the photo where you want it. Not too good.
To top that off, you cant see the photo being moved if you dont have enough screen real estate, so you have to move it blindly until it comes into view.
Sure, its always a good idea to pre-sort before you upload, but changes happen & are inevitable.