I have done a fresh install of joomla 1.7 and Dtregister 2_7_9a to my site, and after testing it I noticed the user panel will not let you edit your registration or cancel your registration. I have asked a couple of people to try it also. They had the same results with follow error message:
Warning: Invalid argument supplied for foreach() in /home/content/html/administrator/components/com_dtregister/models/user.php on line 1866
Could be connected to an issue I've raised too - Users can't manage events (eg CSV export) from the frontend in 2.7.9a on my Joomla 1.7..... I raised a help ticket yesterday... so hoping to hear something soon!