In regards to locating people and contacting them via the forums if they are logged off I suggest that it be possible to rightclick a hearthfire that I find and be given the username of the person to whom it belongs. This would be useful, instead of having to run around defacing rockpiles into runestones and hoping that they find it and read it. It would allow the person to actively seek someone out.
If you wanted to develop it even further why not simply allow me to edit the details held on the hearthfire, I could if I wanted indicate I was never willing to be contacted or trade and remove my username, or add my forum username if different from my game name, even add in hours GMT that I was most likely to be online. There are more possibilities for just a small amount of text like a runestone or limited to data fields that the user would have to fill in.
In regards to exploits; I don't know the intricacies of the game enough but I doubt that only the username would cause too much strife.
Any comments?
EDIT: Also, along the same idea. Identify who the owner of land is when I accidently (or deliberatly) try to cross the border.