My question is regarding that if you do get a background or whatever check from one of those websites would something like that show up on a thorough background check?
I work in a science background and there are several government run organizations that would be a good career move. (just to clarify, in no way is it dealing in LE, its science/research stuff)
I would hate for me to get turned down from these types of opportunities because I went to one of these sites to get checked out.

Glad to meet a fellow paranoid.    
I assure you I use the word "paranoid" here in sincerest of flattery.

I already asked this question a few months ago.  See link (for the answers):
http://www.theeroticreview.com/discussion_boards/viewmsg.asp?MessageID=63844&boardID=33&page=

Trust me don't worry about it. That is all I can say.

as long as you are not ask for your SSN you are ok...

Thanks for the responses.
I guess my only last concern is payment of these sites for membership.  I guess it would make sense to check credit card purchases during a background check but a $12 here and there doubtfully would catch any attention.  Right? :p
Thanks again.

And these charges usually have some generic sounding name associated with them on your credit card bill.  Your cc statement won't say "Date Check"  or "The Erotic Review" on it!

I worry that I may become rich and famous and will now be subjected to blackmail.  If that happens, I plan on going onto Letterman and say that I was horny, end of story.

Check the payment options for the site(s) you wish to sign up for.  Likely some can be done anonymously.  You may get some help by asking for help at the site.