For example, I looked at a postfix cookbook[1]. The client recipe[2] looked nifty but wasn't something I needed, and wouldn't work without modification anyway since I run serverless. Meanwhile one of the key parameters I needed to change was recipient_delimiter, which this cookbook had hardcoded into the main.cf.erb template[3]. I decided to just write my own bare-bones cookbook that didn't try to abstract every single configuration parameter I could think of. I haven't had to modify it since.
This has been a common experience for me in the past year. I have yet to actually deploy a public cookbook.
[1] https://github.com/opscode-cookbooks/postfix
[2] https://github.com/opscode-cookbooks/postfix/blob/master/recipes/client.rb
[3] https://github.com/opscode-cookbooks/postfix/blob/master/templates/default/main.cf.erb