I primarily use TT in my CGI projects. It's not the fastest system, but it's fast enough and very flexible. I've also used HTML::Template, but switched to TT w/ the next release of my project.

My reason was that I (the programmer) had to do too much work to get the data in the correct format H:T required so the HTML guys could do their thing. With H:T I had to do all kinds of massaging because the syntax is very simple (by design). With TT, I just throw data structures at the template folks and they can use it how they want since TT can parse all kinds of data structures.

Just my $.02.