A least a handful.
ever think to look up the fucking word in the dictionary?
http://dictionary.reference.com/browse/substantial?&qsrc=
It's a subjective word, dependant on the situation, facts, objects involved, etc.
What this means, is that your poll is meaningless. It could mean 80% to all of us, but 5% to your boss. You'll only be able to tell what it means by asking the person who interpreted it in your case.
Which is why I am asking all of you what it means to you. So, if your boss said to expect a substantial raise, and he really emphasized the word substantial, what is the biggest number that would make you go 'that is not substantial!' Then pick the next biggest whole number and find it on the list of possible responses.
This year 5% could be considered substantial, many companies are still giving 0% or less.