First I chose to develop my own system so I can customize everything as I want... and also because I enjoy coding.
I used the php/mysql couple for the server side coding (nothing unusual, when I 'll have some time I'd like to try Python or Ruby).
I also use the template engine Smarty, since I've been working with it, I love it : plus a MCV framework the code is really clean.
Design (page HTML) on the one side and server coding on the other side, classic and easy to maintain.
Basically, If you previously visited a website who used Mootools from Google, the access to my page will be quicker, nice saving of time.
For now, Google offers only the 1.11 version of Mootools but I hope they will quickly host the 1.2.
I also use rewrite_mod to have SEO "friendly" Urls...and mainly cause it looks better and easy to use.
As you can see on the top right of the page, this blog supports 3 languages. Clicking on a flag redirects you to the same page translated and not to the top page which is nice I think.
As for the comments avatars, I use some flickr photos under Creative Commons License. When you add a comment and choose an avatar, a link appears. This link redirects you to the photo's author.
I also use a Creative Commons License for the blog itself(link at the bottom of the page).
To fight any spammers I use a class from the Zend Framework to connect to the API of Akismet... will see if it works!
The navigation in this site is really "ultra not unusual"! : the 4 main categories are reachable by the photos in the top menu, and a tag cloud.
Plus, some links "previous articles" or "related articles" will be here and there.
The site is minimalist; I like it like that, I will add other functions later but the design will remain simple.
That's it, for those who read until here and undertood nothing, no worry! : I invite you to read my other posts ;)