You launch the jailbreak app and then it gives you a choice to import text from following apps: SMS, NOTES, EMAILS or Regular files. So basically you have to launch the copy/paste app to go through your SMS, notes, emails or regular files, you can't go directly to your SMS, notes, emails and copy what you want to copy. I was disappointed because the main thing I wanted is to copy text directly from the apps esecially SAFARI! But still, this helps a lot if I want to copy an email to my notes or sms.
As much as I really WANT and NEED the copy and paste feature in my iPhone, there is a good reason why Apple hasn't integrated it into the iPhone. I believe it is because it's not stable. The same with Flash.