I saw that Google is offering the ability to display the QR code of the 
shortened URL by appending a ".qr" at the end of it. It would be nice to 
have this and other functionality inside of the YOURLS application.

I suppose this can be done by reading the last three characters of the URL 
and redirecting it to the QR generator if it is ".qr"? Like adding another 
MOD_REWRITE rule? 

RewriteRule ^([0-9A-Za-z]+).qr/?$ /yourls-qr.php?d=$1 [L]

*shrug* I'm not an Apache expert. Seems to work?

In addition, I believe that the QR code can be implemented into a couple 
other places within your admin application.

I was able to download a QR PHP generator (Swetake - http://pauln.us/57) 
and had great results in doing some trial runs. I modified the YOURLS 
version I was running to implement a quick QR generator from the main admin 
list.

For example, I created a new icon and added it to the actions column inside 
the functions.php. The result gave me another option to click on for a QR 
code generator.

http://pauln.us/58

I then created a quick/dirty QR display function in the insert.js file. The 
end result, was a pop-up box that showed me the QR code for the URL.

http://pauln.us/59

Also, it would be nice to have the QR code display in results after you add 
a URL as such.

http://pauln.us/5a

I will attach my futile scripting changes I did to get the action menu to 
work. Again, I simply installed the above QR generator inside the includes 
folder (/includes/qr/) and then renamed their php script "qr.php" and stuck 
that in the /admin directory. I also stuck the same code in a new file 
called "yourls-qr.php" in the root directory without authentication but 
that seems like the wrong way to go about it. Probably sitting in one 
location will work but not sure how you like to organize things....