It's the private lists that will get you. What do you do if Google has your IP address on an internal blacklist? Or your health insurance company? Or some random Barracuda-style e-mail filtering appliance? Nothing. You're screwed.

In that case, the IP is screwed. I plan change IP, or hop hosts if/when this happens. I opened 6 accounts on 6 different hosts, and only two are active for this reasons. So far so good :)