Miss Lolli the wisee has spoken!! ( :lol ) & it's all true.
You can be found & that info is there forever. That doesn't mean that IT WILL be bad or that bad things WILL happen. It just means, they definitely can & you should be aware of that.
Might be jinxing myself here, but in the 2 years I've been on MFC- only 1 person who I knew IRL has stumbled upon by accident (everyone else who knows, I've told.) & thankfully he was cool about it.. (I mean he WAS a perving premium on the site, really what can he say, right?)
Not everyone has a bad experience with people finding out, but you need to prepared for that possibility and for how you will handle it if it's a negative experience.
There are also some precautions you can take to help reduce (but not eliminate) the likely hood of someone you know irl finding you- like blocking your home state or states where close friend/family live on MFC. For those who are really cautious, make my twitter private, so you have to approve accounts.