Jekyll is absolutely brilliant. There are a lot of static blog generation tools out there but this seems to work best for me. I dont use the github integration much (automatic publishing by pushing to github) but do store my site on a github repo.
The only downside as with any static site solution is comments. I currently use Disqus - I have no complaints with them except that I like to own my comments rather than hosting them with a 3rd party.
I'd love to see a lightweight version of Disqus/Intense Debate--they seem so bloated. No branding, avatars, voting, etc...just simple, fast commenting.
I was using Disqus as well for comments on my gihub blog, but some random reason it started redirecting to itself. Didn't have time to debug it so just removed it for now.
The more semantic you make your HTML, the less that this tends to matter. Right now I'm actually <section>ing and <article>ing my way around my site, so when I want to change the design, I head straight for the one place it's actually described: the CSS.
Not to mention the template mechanism. With my (home made) site generation tool, I changed the whole design of my site by changing exactly 2 files : the template, and the css.
I'm not exactly sure what you mean, but if you run jekyll --server --auto while in development any small change you make gets automatically regenerated and it only regenerates affected files.
The only downside as with any static site solution is comments. I currently use Disqus - I have no complaints with them except that I like to own my comments rather than hosting them with a 3rd party.