CTRL-A followed by CTRL-C allows me to copy the entire post (the one I am currently entering) to the clipboard. On other posts, double clicking in a code snippet copies the entire snippet (including formatting) to the clipboard. Clicking and dragging selects a block of text, then CTRL-C copies it to the clipbooard. No functional problems there.
I typed up a long post and for some reason, Daniweb logged me out.
I imagine what happened is that you were never logged in. If I am not logged in and I click on a link in my email, I am taken to that post. I can start typing a response but I can't post it because I am not logged in. At that point I have to copy all of the text I have entered to the clipboard, log in, then paste that text back into the text area. As far as I am concerned, since you can't post unless you are logged in then you should not be able to enter text.