The offending site will first be warned, and ultimately suspended, if the issue(s) are not corrected.
How will I know if I use too many resources? There is no way for us to predict how much server resources your site will use. If your site is causing the problems, you will receive a minimum of one warning e-mail advising you to correct the issue(s). If you fail to do so, your service will more-than-likely be promptly suspended; again, you will be notified via e-mail.
We will not provide exact details as to how we determine which accounts are auto-suspended because this would lead to clients intentionally abusing the system almost to the point of triggering it, but staying just below the threshold.