It's not in Gentoo Portage yet.
LOL. see ->
http://sourceforge.net/projects/calibre/files/
0.8.17 < 5 hours ago 312 downloads
0.8.16 2011-08-26 10,633 downloads
0.8.15 2011-08-19 6,986 downloads
0.8.14 2011-08-12 6,841 downloads
0.8.13 2011-08-05 6,851 downloads
0.8.12 2011-07-29 7,271 downloads
0.8.11 2011-07-22 7,470 downloads
It takes Gentoo Bugs about 2 weeks to get an EBuild (package install script) into or updated into the package management tree. (Add +6 mos. for other binary distributions.) I think you wore them out with all of your snapshot releases, as Gentoo usually does have the latest and greatest whilst everybody else is stuck with 6+ mos. old binaries.
But, this is such a common task that any Linux folk should be able to reproduce. I'm seeing similar with the display.1 man file too. Seems like all of imagemagicks man files are doing this. (See the error "Failed to find image: ../images/annotate.png" wha?? we're in terminal and man files are text only! ...that I know of.)
Transformed CSS selector h|DIV.tabs h|A to h|div.tabs h|a
Transformed CSS selector h|DIV.tabs h|SPAN to h|div.tabs h|span
Transformed CSS selector h|DIV.tabs h|INPUT to h|div.tabs h|input
Transformed CSS selector h|DIV.tabs h|TD to h|div.tabs h|td
Transformed CSS selector h|DIV.tabs h|SPAN to h|div.tabs h|span
Transformed CSS selector h|DIV.tabs h|LI.current h|A to h|div.tabs h|li.current h|a
Transformed CSS selector h|DIV.tabs h|LI.current h|SPAN to h|div.tabs h|li.current h|span
CSSStylesheet: CSSImportRule not allowed here. [3:1: @import]
CSSStylesheet: CSSImportRule not allowed here. [3:1: @import]
CSSStylesheet: CSSImportRule not allowed here. [3:1: @import]
CSSStylesheet: CSSImportRule not allowed here. [3:1: @import]
CSSStylesheet: CSSImportRule not allowed here. [3:1: @import]
CSSStylesheet: CSSImportRule not allowed here. [3:1: @import]
CSSStylesheet: CSSImportRule not allowed here. [3:1: @import]
CSSStylesheet: CSSImportRule not allowed here. [3:1: @import]
CSSStylesheet: CSSImportRule not allowed here. [3:1: @import]
Source base font size is 12.00000pt
Removing fake margins...
Cleaning up manifest...
Trimming unused files from manifest...
Trimming u'background.jpg' from manifest
Trimming u'tab_l1.gif' from manifest
Trimming u'tab_b.gif' from manifest
Trimming u'tab_r1.gif' from manifest
Trimming u'tab_b1.gif' from manifest
Trimming u'tab_l.gif' from manifest
Trimming u'tab_r.gif' from manifest
Creating MOBI Output...
67% Creating MOBI Output
Generating in-line TOC...
Applying case-transforming CSS...
Rasterizing SVG images...
Converting XHTML to Mobipocket markup...
Failed to find image: ../images/annotate.png