I may be in a distinct minority but I like and use the ePUB version of the User Guide. I use calibre to move it onto my Kobo reader and will occasionally browse through it to learn things I've missed in the past, e.g., when I'm stuck in a waiting room or something. Anyway, there are some things that stand out to me, as a CodeIgniter user (developer) and as a reader/writer/publisher:
1. The file type is not recognized by Chrome when I click the link to download it, so I have to remember to right-click and then choose the download option. I assume a MIME type adjustment on the codeigniter.com site would fix this.
2. The ePUB file lacks a cover, so a) it doesn't stand out from other books on my reader that aren't correctly assembled with covers and b) when I put the reader to sleep with the User Guide active, the sleep display is rather unsightly text instead of a tidy cover image. It looks like Sphinx supports adding covers via the epub_cover option, as of version 1.1, so adding a cover should be workable within the automated file generation routine. I've attached an image (if that works) in case there is interest in doing this but nobody wants to take time to make one (reasonable since it's not a high priority).