What are blogs good at? 

• A blog is a super simple way to be on the web
• A blog makes it easy to keep a chronological diary
• A blog lets you easily link to other sites
• A blog has a very simple yet accepted commenting capability
• Blogs are sorted, ranked, fed and cross-posted to, creating a community

What are lenses good at? 

• A lens is a permanent signpost, it doesn't have to change every day
• A lens can point to your best blog posts, or sort them by topic
• A good lens is about just one thing, so it gets more relevant search engine traffic
• A lens makes it easy to include autoupdating information, like RSS feeds, news and Amazon bestsellers
• A lens can include Google maps, eBay auctions, polls and other features that are tricky to get into a blog
• A lens gets free traffic to your blog
• A lens can raise money for charity, a few pennies at a time. And it's free.

Structure matters (sometimes) 

Blogs are unique. They have different structures. You can't 'get' a blog right away. You need to read a few posts, figure out what they're about.

Lenses have structure. To some people, that's boring. But if you're looking for information...fast... the consistent structure of a lens means that you will find what you need.

People go to a blog and stay. People go to a lens and leave.

Three examples 

Things you could do with a blog (but why?)

Guitars

A lens about guitars, guitar blogs, guitar videos and more

Rajesh on blogging

A starter kit, together with links back to his blog

Softies

Including a pattern for an advanced Himalayan Kitten.