Thomas Klausner has just published the final report on YAPC::Europe 2007, with plenty of statistics and details. Note that this was the largest Perl conference in Europe so far, and that it generated tens of thousands of pounds in profit.
If you’re thinking of organizing a conference, browsing the details there will help. In particular, the timeline of planning events is a good indicator of what any community-organized conference will face. I’m sure YAPC::EU 2008 will be even better thanks to all of the work the Vienna team has done.