There are numerous posts in the forum here about 1.6... including discussion in the last few days. Our 1.6 version is going to be out by tomorrow! Watch our site, twitter, facebook, email...
I have installed current version DT Register 2.7.8 on an existing J1.7 test environment and first basic tests seems to be successful while there is an issue with the JomSocial plugins when they are enabled. Then I have blank screen.
So I am also looking forward to get an ETA when the supported DT Register Release for 1.7 will be available - because on joomla.org you can read that Version 1.6 has reached end of life on 19 August 2011 and all users of version 1.6 should update to version 1.7.0 before that time.
So therefore for me DTRegisterJ1.7 readiness is top priority
Let us know whether we could help you to perform some UATs on newer versions to accelerate the support of J1.7.