[cdawzrd]

Until there is a open-source program that replicates what Ableton Live offers (seamless and easy-to-use integration of audio recording and nonlinear editing with MIDI production), no one will consider using an open-source tool.

The biggest hurdle from my point of view is that low-latency audio on operating systems that are not Windows or OS X is a joke. Some organization needs to sink and huge chunk of developer time into either improving the user and developer experience of JACK or writing something new. Maybe once that is in place and starts shipping in vanilla Ubuntu (no special kernel requirement either!) the user software developers will be able to start catching up with the tools available on the Win/Mac platforms.

[koide]

Easy to use? I've played with some of these tools, including Ableton Live and I've never found any that is actually easy to use.

They are all too stuck in the sliders/knobs metaphor. I'm not sure it's an adequate metaphor for people who has not produced in the physical world before.