Joe O, I think there is a key that can turn the client off, just like they used to switch you automatically from one contest to another. There was also the method of putting a "shutdown" file into the same directory as the client, but that isn't practical for anybody except personal herds.
I have put most of my UD clients on hold for a few weeks/months. I want to be in on finishing this to 100%.
If it goes past 100%, I will not continue. That is a possibility, especially with a lot of the hacking attempts by teams a few years ago (remember the big Russian team fiasco?). I have no trouble believing that it is in the last 17% of keys. My biggest problem is that keyspace is SO FRAGMENTED, I can't get any big blocks anymore. They are all 2's and 4's and 6's in size now.
My PProxy buffers just don't last very long for my sneakernet machines and the "expertmode" switch doesn't seem to work.