Samuel Kordik recently named Backpack his website of the week:
It is slick, flexible, and super-cool. In fact, it combines the total flexibility of a paper-based notebook with the infinite re-writable possibilities of electronic data...Backpack is one of those no-brainer tools that hides mindblowing capabilities. It actually significantly reminds me of an Apple application. It just makes sense...
What do I use Backpack for? To run my life. At this point in my life, it makes sense to have things online. I have internet at work and in my room, and so it provides a handy central point to run things through.
I use a page for each of my action lists, and then a page for projects, a page for Someday/Maybe’s, and a page for Notes. This flexible solution works quite well for me and is well worth the paltry $60 a year price tag. Which is about what I paid for my planner in previous years.
We contacted Samuel and he gave us some more info on how he uses Backpack:
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I create rules in my email client that automatically forward different items to my Backpack page. This is especially great for emails with attachments since the attached files are automatically placed onto the page.
I've attached two screenshots that demonstrate three rules that are examples of the kind of rules I use.

1. (See Gmail screenshot above): Any thing emailed to my address & +action@gmail.com automatically gets forwarded to my Backpack inbox, skips my Gmail inbox, and gets labeled "_ACTION" in Gmail. I use this a lot; so do others. My supervisor, my friends, etc. can virtually place something in my Backpack inbox by emailing to that address.
2. (See Gmail screenshot above): Specific projects get their own Backpack page, and here I've setup a rule that scans for keywords, labels it in Gmail with the project tag, and forwards it to the project page.