From my personal experiences; and talking to one of the employee's in the IPS company, IPS doesn't majorly care about nulled software; as long as it isn't generating money on a substantial amount. Don't get me wrong; they may still take action against your site but regardless as Phun and Davlin have already said; Size is a HUGE factor when they are considering taking down a forum.
Recently one of my friends has needed to take down their forum because IPS thought it to be able to make enough money to buy a proper license; yet it turned out that my friend was only running it for entertainment purposes; after a couple of months, the site was still up, IPS didn't take any further action; maybe because it takes time. My friend stopped running the site from June; but it is a prime example that IPS are still human and they understand that some people can't pay for things so they go to nulled software. While many companies aren't like IPS; always money grabbers and such. IPS show humanity and compassion all the time.