Disclaimer: I may never use github the way it is intended. I have plans to share gems and projects that may involve collaboration, but I suspect most of my "projects" will be little more than code showcases.
For reporting, I had to humanize various numbers for callouts. I had trouble getting ActionView helpers working, and I was concerned that even if I could get them working, I might have to use substitution to get the desired format anyway.
Hacking number formatting seemed easy and fun, except that this is one of those problems that always seems solved -- and then you run a few reports and discover edge cases that force you to start over again...
It should only take a few moments to see how this works, and I cannot imagine how it could be simpler. One idea might be to extract a method that returns the three digits (case statement from humanize_number), and use that to improve readability.
Macintosh-2:~] direwolf% ruby --version
ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin10]
[Macintosh-2:~] direwolf% ruby [...]/pretty_numbers/format_numeric_callout.rb
Representative numeric callouts...
888 => 888
1001 => 1K
1009 => 1.01K
2112 => 2.11K
20999 => 21K
2099999 => 2.1M
666666666 => 667M
66667868898 => 66.7B
6666786889886 => eep!