>(Note: could use the dates of first Yukkuri threads on poolshmer and 4chan)
Don't know about 4chan, but the first Yukkuri thread on pooshlmer came about on February 2, 2008. Also worth noting is that the first use of "Take it easy!!!" (in JUNK's translation of this yukkuri strip by Makako) was on April 6, 2008.
Screeny is here: http://en.wikipedia.org/wiki/Touhou_Project#Reception_and_fanworks
- [ http://koroinu.com Artelus]