First I would use google suggest to figure out what gets asked around a given subject.
So lets's say programming
Go to google and type in
what is the best programming
then you will get the following
This will allow you to write debate topics that a lot of people are looking for on google and therefore you will rank higher.
Second of all I would go for some more meta questions. The subjects you have are kind of hard to have an opinion about as it seems like most of those subjects can be proven.
So instead of C++ it could be what is the best programming language for X
Instead of Photoshop then it could be Photoshop or Fireworks what's best for Wireframe design.
Make sure that you have one entry point and that this get's people into the disucssion right away. To many debate sites make the mistake of creating all sorts of channels before they have the users.
It's simple math. If you create 3 channel then the chances of people meeting on your site is just much smaller than if you have 1 channel. With time the need for channels might arise but in the beginning make it simple. Not unlike how this stackexchange site works.
Interface is brand, communicate with the features rather than through abstraction. Hope this was helpful.