Back years ago, II gave bonus weeks if you deposited a highly-demanded week. RCI did not in general. However, some resorts, as part of their contract with RCI deposited lots of unsold weeks with the understanding that when their owners deposited a week, they would also receive one of these extra weeks back as a 'bonus' week. Many RCI owners mistakenly thought these were coming from RCI as a reward for depositing their highly-sougt-after week instead. So there used to be lots of confusion as to whether RCI did or did not give out bonus weeks. We don't hear much about this any longer - I guess most of these extra weeks have been used up by now, and developers largely do other things with their extra weeks now.
II's 'bonus weeks' are now 'accomodation certificates'.
RCI, on the other hand, a few years ago started sometimes giving 'one plus one' weeks. They seem to relate, not to what you deposited, but what area you exchange into. These have some limitations on them and can only be used by calling into a vacation counsellor (i.e. can't reserve them online).
See this entry in the RCI FAQ file, available via the ASK RCI forum here:
http://www.tug2.net/advice/FAQ-AskRCI.htm#_Toc32570618
In addition, they use the term 'Bonus Vacations' for weeks that you can rent from RCI, thus further confusing things. See this entry in that same FAQ file:
http://www.tug2.net/advice/FAQ-AskRCI.htm#_Toc32570612