Curious myself, we've got an open registration occurring right now and would hate to risk bringing it down due to a version incompatibility. On the other hand, it's probably best to update no matter what the consequences for integrity purposes.
I had found no issues with my testing on a dev copy site, so I deployed 3.3.4 to the live site.
So far so good, the only issue I found so far occurs when people register with paypal, when they click the 'Return to website' link, it has a bogus URL that gives a 404 error. I don't recall seeing this before, but it still might not be related to J3.3.4. I have opened a ticket for this.
Yes, I have installed and tested 3.3.6 on my dev site - it seems to behave pretty much the same. I have found no difference in DTR from upgrading J3.3.4 to J3.3.6 in my setup. Live site is now running 3.3.6.