I'm Gary Cunningham-Lee, in Chiba, Japan.
The first site I used Tiki on was the now-defunct Phoenix Developer Consortium web site (Wayback link for April, 2003). I also used Tiki for the Japanese site of Genesi SARL for a while; it had a custom theme and was bilingual.
I have a website for Tiki themes at https://zukathemes.com, which is currently closed until I get more themes updated and added, which should be pretty soon. Of course, this site runs on Tiki.
I also started up themes.tiki.org along with Marc, and this came about as a result of good responses to Zukakakina.com. Themes.tw.o is usually running the current stable version.
Over the years, I've worked on quite a few Tiki themes and sites. One that stands out is Mozilla Firefox Help and Tutorials site, for which I "Tikified" the designer's graphics and then worked with Nelson Ko to implement functionality desired by the Mozilla support team. This was a good learning experience for me in terms of file management and so on (thanks, Nelson) and it made me more aware of the need for Tiki to reflect good Web standards (thanks, Mozilla people). (They have since moved to an in-house-developed support system.)
Subversion commits as tracked at Ohloh — this page shows the record of contributions to Tiki's development files in a neat way.
In the past there was a lot of redundancy of files between my custom themes and the Tiki core files, but gradually this is being reduced so, happily, there are relatively few custom files in these new themes, and there will be even fewer in the future.
Due to many improvements in code and a lot of thinking about and discussing of themes and CSS, making custom themes and modifying existing themes is much easier than it used to be, and this development has been a lot of fun to be a part of.
I hope more people will share their own experiences with changing the look and functionality of Tiki sites.
I've done a few documentation pages but would like to get more active. I joined the Editorial Board and hope to help work on the docs project more, but themes have been my top priority.