As with any template builder, this would be great for a new site. If your blog is established, customised, and loaded with goodies, you may have to cut and paste a bit, but this is still a cool tool. It has built a great-looking (at least IMHO) template for Freshblog. I am still recovering from the sting of an inbound that said something like "bad layout, good content," and when I set out to fix the CSS in the template header it became a bit tricky.... Hopefully now the standard of the layout approaches the standard of the content.
There may be (will be?) bugs. Please leave me a comment. I'll be grateful for the heads-up. Font size, link color and such are on trial for the moment, and if the links are hard to find I'll choose a different shade of blue!
So. If you're starting out, and you want a slick looking template such as this, try PsycHo.
You'll find an easy interface that reflects your changes in real-time, and sub-divides the menu into the components of the page so that you can tackle one set of formatting at a time. There are also a number of spiffy export & share functions. Very good stuff.