I've finally created a custom theme for this site and I'll try and give you some insight into how I did it. It took me 1 hour 51 minutes and although I was actually aiming to finish within an hour I'm happy with the time. I know theming probably shouldn't be a race, but why not test yourself! Also, my main goal was to get something original up as quickly as I could so I can make tweaks in the coming months.
I've based my theme on the new Zen template, which is becoming one of the most powerful ways to build a themes in Drupal. This is the first time I've used Zen as a base and it's a great way to go. In the spirit of CSS Zen Garden, Zen is designed to be exclusively programmed using stylesheets. The only tweaks I had to make elsewhere were in node.tpl.php where I changed the default ‘Submitted by...’ text and removed the ‘in..’ text before the taxonomy.
Here's a video of the first 30 minutes of work (my screen capture program lost the rest...):
There are some limitations to my new theme though. It looks great Firefox 2, Firefox 3, Safari 2, Safari 3 and Opera 9, however it currently fails in IE7 and IE8. Didn't get a chance to look in IE6 yet but I imagine it's not good. When I get some time I'll fix this up, with the biggest problem created by absolutely positioning the mission statement into the head.
One other limitation that will need fixing is that I used Myriad Pro in the header. This is a nonstandard font and I should use an image replacement to be sure I get the look I want. The only other font used is Trebuchet MS, which should be fine across most platforms. In both cases I've set Arial as my second font.
Because this is based on Zen, it passes validation for XHTML 1.0 Strict. I only get CSS validation warnings for having one CSS3 property used (word-wrap: break-word;) and having background color the same as color, which is visually fine.
Overall I'm happy with my new theme and it will only take a little bit longer to make it cross browser compliant and good to go.