1. You get all 3 formats
2. You get constant updates to the book (errata and such) [edit: not new editions.]
3. You can connect your PragProg account to your Dropbox so that your books are delivered there automatically.
#3 is a new addition, but it's killer for me. I get all formats uploaded instantly to Dropbox, so they're available on all my devices. And when I buy a Beta book it gets updated automatically without me having to remember to login and redownload.
On a related note: I know this is ridiculous but I wish I could purchase book diffs upon the release of a new edition. I already read the second edition of CLRS and paid $60 for it. Now I just want the new bits of the 3rd edition at a reasonable price.
1. DRM-free formats
2. A support forum where you can ask questions and interact directly with the author
Update: It's under 'edit profile' right before the last listing about Kindle settings.
Designed for Use: Create Usable Interfaces for Applications and the Web
Lukas's blog posts (http://ignorethecode.net/blog/) have appeared on HN many times, and I have made a mental note to buy his design book.
Technical Blogging: Turn Your Expertise into a Remarkable Online Presence
Antonio has also posted on HN. I've been on the fence about this book, not sure if I need it, and I decided to pull the trigger and buy it.
So I am now the proud owner of these two books.
[edit: I think I might also get SQL Antipatterns http://pragprog.com/book/bksqla/sql-antipatterns after recognizing one in my own code. And Web Development Recipes http://pragprog.com/book/wbdev/web-development-recipes. Am I done buying yet? Great deal.]
Disclaimer: I'm an author for the prag prog.
Too bad they do not publish the actual Pragmatic Programmer book.