Wikipedia implies strongly that The Chicago Manual of Style, as well as the MLA and the Bluebook, have different syntactic rules for using ellipsis within a sentence versus at the end of the sentence. That makes no sense if Retric is correct in his/her claim about ellipsis only being licit at the end of a sentence.
These sources appear to confirm my uneducated belief, which agrees with btilly, that ellipses may be used to mark any omission, of any size, including within a sentence or spanning sentences (wp's comment on CMOS implies omitting entire paragraphs is legal).
http://en.wikipedia.org/wiki/Ellipsis#In_English
Also, I have no CMS subscription, but here's a public-facing FAQ that seems relevant:
http://www.chicagomanualofstyle.org/CMS_FAQ/SpecialCharacter...
These sources appear to confirm my uneducated belief, which agrees with btilly, that ellipses may be used to mark any omission, of any size, including within a sentence or spanning sentences (wp's comment on CMOS implies omitting entire paragraphs is legal).