Today's Dilbert (12/01/10):
Here, the -itute of prostitute is serving as a blend component, but could it end up becoming what Arnold Zwicky has helpfully dubbed a "libfix" (a "liberated" word part that yields new word-forming elements)? I doubt that -itute could be a productive libfix, because without the proper context it could be easily misconstrued as a libfix for some other word with the same ending, like institute or substitute. In the case of the collegiate blend sorostitute (sorority + prostitute), all but the initial p of prostitute is represented in the blended word, making the lexical source much easier to recognize.
There are also ad-hoc blends that use the first part of prostitute, such as prostidude (as we discussed in a post last March) and prostitot. In these cases, prosti- is a big enough chunk for the blend component to be properly identified, meaning that it has the potential to achieve libfix status.
Given the popularity of Dilbert, I could see frienditute gaining a modest following, but don't count on other X-itutes to follow suit.
(Hat tip, Nancy Friedman.)