First, the cons:
- Blogger doesn't like <p>. Not only does its editor use line breaks (<br>s) instead of paragraphs, but it seems to strip out the <p>s I add manually in the HTML view.
- The Dashboard interface takes some getting used to. It's not that bad, but it could use some improvement in both usability and aesthetics.
- The Blogger header appears over every page. I've read that it's possible to turn that off, but I haven't yet played with the service enough to figure out how.
- There are only about six templates available in the template designer.
- Only 10 additional pages are allowed. I imagine that's plenty for most blogs, though.
And now the pros:
- Templates are extremely customizable. Each template already includes several variations, page elements can be rearranged at will, and the template designer allows even further customization of colors, sizes, etc.
- The template designer also allows custom style sheets (CSS), which is a pretty powerful tool.
- Custom HTML. Now that's customization!
- Custom templates can be uploaded. Just in case the custom CSS and HTML weren't enough.
- The number of settings and options other than template customization is pretty impressive, too.
- OpenID comments are supported.
Disclaimer: Though I've tried to avoid it, I'm sure I am guilty of mentally comparing and contrasting this fine service with WordPress.com. Once I've had more time to learn the ins and outs of each service, I'll try to write up a real comparison.