You, like me, have a github pages powered blog.
You, like me, are contemplating switching to WordPress for tags/categories.
Fret no more. I added categories to my github pages powered blog today.
You can too.

Just assign a yaml list to categories in your page meta:

categories:
- ruby
- rvm

Listing and linking to them was harder than I expected.
I was forced to create a page for each category that I wanted a list of posts for (code.html, ruby.html).

Update: I went to great pains to format this liquid code (within liquid). Even using the --safe argument on my jekyll server. But, it still formatted differently on github pages. I hope to figure out a workaround shortly. Until then, check out the source at github.

For each post, I expected to get a nice list of assigned categories using:

{{ " {{ post.categories | array_to_sentence_string " }} }}

instead, I got:

nothing

Then I tried this (and variations):

  In this post:

    {{" {% for category in post.categories "}} %}
      <a href="/{{">{{" {{ category[0] "}} }}</a>
    {{" {% endfor"}} %}

Which rendered:

  In this post:

That's right. Nothing.

sites.categories works nicely in that loop, but I wanted the categories for this post.

In this site:

{% for category in site.categories  %}
  <a href="/{{ category[0] }}.html">{{ category[0] }}</a>
{% endfor %}

Armed with this knowledge, I set out to create a Tag Cloud. But, I could not find a way to get the count of posts for each category.
I found an example on litanyagainstfear.com. Alas, it looks like you have to name each category explicitly to get the count of posts.

{{" {{ site.categories.code | size "}} }}
{{" {{ site.categories.ruby | size "}} }}

Which led me to the (poor man's) Tag Cloud you see in the upper right corner.

The good news? I was able to use _includes to reuse the category page for each category.

See the source for this page at github.