* Your minimum TTL is 60 seconds, but you only learn this by trying to set it to something lower

* I actually like Hurricate Electric's interface better: there is much less clicking to do. Their updates are also instant.

* You lack IPv6 support (both AAAA record types and, from what I can tell, IPv6 connectivity). This is really important and would be a blocking issue for me.

* The REST API is something HE doesn't seem to have so good job there.

* You don't have HTTPS available, yet you have a authentication and management system. This is broken and would be another blocking issue for using your service. <rant>Browsers should display a big fat warning next to each <input type="password" /> field that is not served over HTTPS. In 2011, not having HTTPS set up should be a #1 bug.</rant>

Otherwise, looks pretty cool. If HE ever changes their services, stops being awesome, I will keep you guys in mind.