This is exactly how I cut my own hair. I started doing this in August and I've cut my hair this way three times now (once just this morning!!) and I love the look it gives.
When I did it the first time I cut only an inch at a time, afraid I'd chop into my length. But, while bending over, I grabbed a strand of my length from the nape and followed it down over my head to it's end and found I had a good 4 inches or more before I'd hit my length. So, the second time I cut it, I cut about two inches off. And just today I cut another inch or so. I think I've still got another 2.5-3 inches before I reach my nape hair ends, but I rather like to cut it inch by inch every few days so I can see how it appears dry before going at it again.
But, I really like the way the layers look with this method. I don't use the ponytail, however, I just bend over and comb all my hair over my head and secure it between my index and middle finger (like stylist's do when cutting hair) and snip away. Maybe next time I'll try the ponytail; I'm just worried it will somehow make some hairs uneven.
Does it work better to do this method with dry hair?