Also I think it is a lot more than %5. Also, again, I think it is still OK only if the half percent of the users represent the real (not-spam) users. The spam users are increasing and becoming much harder to determine when the user base grows. Even if you're running a simple blog and you notice lots of spams in your comments when you get some traffic. %5 is just not a realistic value.
Also lets not forget about "the paid" users. There is such a thing behind the scenes and they are not spam/fake.