Hello everyone !
I'm glad to announce that it's working properly (more or less ?) under Linux !
The source is available here :
https://github.com/toine512/jtv-downloader
You need Qt 4 to compile it. I don't think there's up to date rtmpdump builds in Debianish repos, so you have to build it yourself too ...
@KSV Could you change the topic name for "Justin.tv live downloader" ? Thanks.