In reply to pasbury:
I've been slowly working my way through the Welsh and English Nuttalls for about 15 years now, I only really walk in winter (summer is for rock climbing) and when there's no winter climbing to be done.
What I like is not that the "unknown" mountains are anything special in themselves, although a few are, but that it forces me to places I've never been. I've discovered new towns and villages en-route, learned more about local history and interesting events associated with these areas, seen wildlife you don't see as much in the busy areas, had whole days to myself instead of jostling with the crowds and my overall feel for the geography of these areas has improved massively.
There's a lot more to walking than just ticking summits.
Just bear in mind though, that by the time you've reached the end of the list they'll probably have discovered some more, there's a dedicated army of Nuttalls enthusiasts out there surveying lumps and bumps in the quest for new summits as we speak!
Keep an eye on their website for updates.