Fosdem

in Brussels (Belgium) is one of the largest, probably best OpenSource conferences in Europe. A link to the 2005 event:

http://www.fosdem.org/2005

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TheoVerelst happens to present at the Tcl Developers room if all goes well: http://www.fosdem.org/2005/index/dev_room_tcl .
I've made a page about the 2004 conference: http://82.168.209.239/Fosdem/