I just reached the halfway point in my current project; rewriting a 100,000 word story.
The story, code name TAVOG, started out as an adult SF/Fantasy mashup and I fought with it from the minute I finished the first draft. It didn't want to be edited. It was like pulling teeth without anaesthetic for me. Who can guess what it was like for the story.
Anyhow, a very competent editor associated with a major genre publisher cast an eye over it, came up with a couple of very good points, then pulled the pin out of the grenade and dropped it on the table. "This would probably work well as YA" sez he, over his shoulder as he heads for the hills.
So that's the project. Rewrite 100000 words into a YA story. Easy? No. The original story was written from three different points of view, two of which were very much 'grown-up'. Now there may be a YA novel out there somewhere that fits that model, but I've not seen one. Ripping out two points of view and rearranging the story cost me (so far) 22,000 words, one awesome character, and a lot of skull sweat.
Having said that, what's coming out of the process is really exiting, and I'm sure its going to be a much better book when its completed. Never let them convince you writers don't need editors :)