I'm late to the party, but could everyone answer me this- how often does you're public IP actually change with any of your ISPs??

With the numerous companies I've used, the ONLY time I've ever seen my IP change is getting a new modem through, say, Comcast or whoever. It goes by MAC address, and if you use Comcast and then set to bridge mode and use your own device, that's a new MAC so you'd get a new public IP. Swap ISPs obviously a new IP.

I've NEVER randomly received a new IP when using the same equipment consistently, so I'm not sure why everyone's so worried about dynamic DNS stuff.. Maybe outside the US is different? I've lived in a few States and it's always the same. If you make a hardware change, just note you should also double check your IP and update it, that's all.