A follow-up on my previous post about 々, the kanji repetition marker. As I elaborated there, as long as certain conditions are satisfied, it's preferred or almost obligatory to use 々 instead of repeating a character. For instance, although dictionaries may list the word tokidoki 'sometimes', a redoubling of toki 'time' as 時時, I think it would be rather unusual to write it in ordinary present-day Japanese this way -- 時々 is very much the norm. The only real results of Japanese google searches (try it yourself) for "時時" seem to be dictionary entries and examples like mine in the post below where two 時 occur adjacently but are not part of the same word. Chinese, by the way, simply repeats characters without using a marker like 々. Chinese xièxie 'thank you' -- a redoubling of xiè -- is, as far as I know, always written 謝謝.
All this said, there do seem to be exceptions in Japanese, or at least one. There is a fairly common adjective, samazama 'various' 様々 which is a redoubling of sama 様. As expected, this uses a 々 instead of repeating 様. Notice that the result of sequential voicing (rendaku) is that the second /s/ becomes voiced. Quite by accident, I recently became aware of another word, a suffix, -samasama (note the absence of sequential voicing). The context is this: in the short piece "I'm a supporter" (ぼくはサポーター), by Amano Hirofumi (天埜裕文), the author talking about the way in which Barcelona supporters apparently turned on someone named Figo after his move to Real Madrid.
…「裏切り者！」なんつって、スタンドから物を投げつける、なんてこともあった。それまで「フィーゴ様様！」だったくせに。（『すばる』2010.8: 134)
... some people even shouted "traitor" and threw things from the stands. In spite of the fact he'd been "the Great Figo [Figo-samasama] !" up until then. (The Subaru Monthly 8/2010: 134)
