Cairo 1.0.1 have PS/PDF backends in addition to PNG and glitz which are already supported by cairo-1.0.2.ebuild through use flags. This patch adds support for ps and pdf too (you may need to add use.local.desc for 'ps', i'm not sure about the name). Tested with dia-cvs and it uses pdf/ps backends well.
Created attachment 78840 [details, diff] cairo-1.0.2-r1.patch
Upstream does not consider ps/pdf backends as stable yet, will revisit when they do