Yup, you are right. I was testing with /var/log/messages itself, which would cause "head -n1" to run as fast as the Kindle can, as I didn't want to change the config file.
Yeah, there is no reason why the Kindle can't do no flash updates, in fact it does when you move menus and other little things that have to be done quickly.
I've combined the two methods now and it works perfectly every time (unless you change the page really quickly.)
First it waits for a key then it checks if a book is open then it checks for a change in /var/log/messages (the pipe method is much better but I can't think of a better method that won't require changing a system config file)
It should work perfectly in menus outside of a book but it will mess up book menus.
Anyway here they are:
Progress bar remover