When Trello came out I had been working on ThetaBoard for a while. Both products draw heavily from some Kanban tools that have been around for years.
If Trello had been out earlier I might not have started my project. That being said, I'd argue that the UX/UI and aesthetics of the two apps are different. I'm going to be making some improvements this year that will differentiate a bit more. As long as people keep using it, I keep plugging away at it.
otherwise, it seems neat, but i def trust trello more with my data. thetaboard terms and conditions could actually have some content :\
The comments issue was a tough decision. In the end, I wanted to keep everything on the card itself and do my best to reduce or eliminate/reduce modal windows and drop down menus (I have some but they are few and far between).
I'm actually a fan of Trello myself and use it for some projects--I'm sure Trello will be around for a long time. I am actually ramping up work on ThetaBoard this year (it's been nights and weekends for the couple years) so there is no danger of it going away any time soon. And I'll work on my terms & conditions!