The prawnto plugin is ready and live on Github , albeit without much documentation.
I created several Rails applications that put the beginning and the beginning in PDF format, and I can definitely confirm that Prawn / Prawnto is the way to go. The DSL provided by Prawn is really elegant and enjoyable to work with, and although the library is not as functional as the others, it handles most of what you need out of the box without any pain.
I saw Gregory Brown (author of the Prawn library) talking about the Ruby implementation, and he was a JRuby user. I would be surprised if you find any problems there, although I personally have not used shrimp with JRuby.
Prawn Google Group is relatively active and useful, so you can also check it out.
It appears that the Prawn site is still available.
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