Jeykll is a static generator which has simple support for blogging. If you get started with Jeykll, you still have to write all your own HTML, CSS, etc. Getting a Jekyll blog from just a generator to the point where it's something you'd be proud to post takes a good chunk of time and many developers don't want to deal with designing their blog.
Octopress isn't really any more complex than if someone set up a Jekyll blog for you and handed you the keys, but of course it's going to look complex when compared to a generator.
I'm using Jekyll, and it took me roughly 3 nights to get it all up and running. Now looking at Octopress, they've literally done a couple of things I did myself to Jekyll (new post rake task, uploading to production, etc. etc.) So if I'd start from scratch today, I would take a good look at Octopress indeed.
From whatI can tell from the git repository (https://github.com/imathis/octopress/), Octopress adds two major things to Jekyll: a bunch of automation (via the Rakefile) and a default theme.
Reading through the Rakefile, the automation actually looks pretty useful. For example, you can a new post with rake new_post["title here"] and Octopress will generate a properly named file for you with the correct yaml front matter.
I didn't look at what the default theme actually looks like, but looking through the code it appears to be useful in quickly getting a blog up. For example, it has a partial for integrating disqus comments out of the box.
So what makes it for hackers? The Github backend? Including a plugin for code by default? http://redraftable.com is a blog engine for hackers, other than the author won't release sources while the project is still immature.
That's how I always used Wordpress, but it's not exactly elegant. You always have to make little edits in a small textarea box. No syntax highlighting. Need to submit the entire article to save (instead of command-s). You lose your cursor position when you save (super-annoying with longer posts). Wordpress doesn't support markdown natively. etc.
I didn't knew about redradtable, it looks interesting, thanks for the link.
[Disclaimer: self advertisement follow ;-)]
I think that my own blogware fugitive is by far more hacker-friendly than octopress. It only depends on git and it integrates completely in the normal git workflow by using hooks to generate static html from files. Also, the article files just contain their title (the first line of the file) and then the article itself. All the meta data are those from git: creation and modification dates, authors...
I've been using Octopress for a few weeks now and really like it (I stumbled across it on github and started using the new version before it was released).
Static site generators are great, but you still have to do the design, which is a non-starter for a non-designer like myself. With Octopress I was able to get a great looking, Jekyll-powered blog up and rolling as easily as using Wordpress.
I'm still a lot more impressed with the Python spinoff of Jekyll. It's called Hyde (http://www.github.com/hyde/hyde) and in my opinion a LOT more functional. I do wish that the documentation was a tiny bit more complete though.
If I were going to make a new site based on Jekyll, I'd seriously consider Hyde instead.
The really nice thing that I personally like about Hyde is the fact that it is very component based. For example, it uses Jinja2 for templating. Which is extremely similar to Django templates. It really is a nice little setup that let's me do some neat things very easily. Very powerful.
Another thing I like is that Hyde will regen only the files needed to be regenerated. You can of course force a full regeneration of the site, but as your site grows (particularly blogs) the slower regeneration gets. This means that for simple things like adding a new post to the site can mean very quick regeneration.
Jekyll is certainly an inspiration, but it seems to be lagging behind in basic functionality of some other more interesting projects.
This looks nice. :) Haven't had a chance to try it yet, but it looks very promising. I very recently built a jekyll blog, and while playing around with the CSS was fun and educational, my blog seems kind of shabby in comparison with wordpress blogs and the like, and I don't know if I'd be able to get my design skills up to the point where I'd be able to make my blog look that good.
The most surprising thing and biggest issue I can see right now is that there's "a" theme - I was expecting several. But I imagine that there will eventually be support for more (user-contributed) themes. I also like the syntax highlighting (I think pygments looks kind of ugly), although I'd also like to see more support for customizing the highlight appearance, like maybe removing the background.
If you're already using Jekyll, you might consider moving to Octopress if you like the design, plugins, or rake tasks. It's MIT licensed, so if you would rather just snag those and integrate them into your existing blog that's fine too.
There's no official affiliation with Github. I started thinking through the branding for Octopress in 2009 when it first came out. I was looking for a good mascot and around the same time David Lanham did his 'Bubble Bay' design for a firefox campaign http://davidlanham.com/art/bubblebay/
I started thinking that an Octopus would be a great mascot. They're intelligent, flexible, and have loads of personality. And I asked David to do the artwork for the logo.
The 'press' part was taken from Wordpress, but mainly because I really like how subtly different it is from Octopus.
"TCP/IP won because we focused on writing the software, not the documentation" - Vint Cerf 
Hackers write code. If you write code and documentation, you're an engineer, good programmer, etc.
Think about what you are you saying when you're "hacking on some code" -- you are intentionally writing code that is bad, but cleverly bad enough to get the job done. "Thoroughly documented hacks" are about as nonsensical as F. Scott Fitzgerald exquisitely writing about how great it feels to take a piss.