I wasn't at RubyConf 2004 (back then I thought Ruby was some weird Perl-ish language from Japan, not worth my attention) but for my RailsConf talk I dug up some old blog posts about what it was like when DDH first spoke about Rails at that conference.

Jamis Buck was there: http://weblog.jamisbuck.org/2004/10/2/rubyconf-day-two

Francis Hwang: http://fhwang.net/2004/10/03/RubyConf-2004-Day-2

It's amazing how few people were there and how marginal Ruby was in 2004.