The port opening is just to let Minecraft through the wires, like how firewalls need to be allowed to run certain games or programs to let them update. If you have a port open people can only access what you have opened IN that port...IE: Minecraft. Most routers block X number of ports by default because the average person doesn't need them all opened (and it's a good security measure, like having virus software).
An IP address is basically just a big fangled "Internet phone-number," nothing less and nothing more. By itself, the IP-address reveals nothing at all about the computer you're actually on (That comes down to needing other numbers that relate to YOUR computer, which is something different entirely). Between everyone in the house here we grand total five computers over three different operating systems and we all have the same IP address because we're all on the same internet. If anything it's probably only going to tell someone who your internet provider is and that covers a lot of geographic area so it doesn't mean much. So, it's not like you're giving someone your home address to your front door. In the grand scheme of things it MIGHT tell someone you live in X country or X state. And you're assuming someone's going to take the time to do all this in the first place. Saying "I use Comcast and live in Tennessee" would likely be just as effective.
Corporate IP addresses, though, are a little different depending on many things.. since most of their internet is set up in house.
And in the end... it all comes down to having a trusted firewall to guard the ports anyway. I'm probably the least worried person about that sort of thing, though all in all. Yes, potentially there's the risk that someone COULD do something, but you have just as much chance of someone using your social security number at any given time. The average person like you and me wouldn't bother. If you're not being ridiculously stupid with it it wont do much.
There's other things you can do to 'hide' like set up Simple DNS Zones if you own a site so you don't need an actual IP, which is what I had been hoping to do..mostly just so people didn't need to remember a big long string of numbers (and I don't plan to live here forever). It involves typing in a "website" address instead of IP.....buuuut I think I set up mine wrong since I'm the only one who seems to be able to connect to it. XD
Or there's always the "Pay a Minecraft hosting company" option, too.
That depends on how permanent you want to be, too. For just BKCers I basically tossed it out there and said go to town.
/Likely TMI from the Think Tank
Happy Forum Games! And may the mods be ever in your favour.