I used 3/4" holes as well. I have a twinscrew tail vise with two dog holes in it; I drilled my bench with two rows of dog holes (in line with the end vise) spaced about every 4" the length of the bench. This way I don't have to spend much time running the vise in and out when I need to use the holes. I also drilled a few more holes about 18" spacing down the center of the bench. So far I've had a hole wherever I've needed one. Have not had any problems with too many holes.
3/4" fits the Gramercy holdfasts (excellent), Veritas holdfast (very nice), as well as most common round dogs and the Veritas surface clamps pictured above (very nice also). I'm not sure I ran across many 1" work holding devices.
Having said all that, I find I do most of my planing with stops, instead of clamping with the end vise and the dogs. I primarily use the dog holes with the holdfasts, so I probably could have gotten away with fewer holes. But, I figured while I was drilling, why not. I still don't see much of a downside to having ample dog holes.