Can some one tell me how famous is this manga or at least how popular. I started to wonder because usually most manga don't have fanfiction or clubs. Unless they are popular. And lately there are. When I started reading it, it wasn't that popular. So can some one tell me? Also how long do you think they should keep it up until putting it into a conclusion?

Erm...very popular? especially among the ecchi-fans :\

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Everyday I'm tumblin'

Maybe its popularity can be roughly measured by the amount of hentai doujin that is based on it:
There are 26 hentai doujin chapters according to my source. With currently 132 chapters of the actual manga, that results in a hentai-rate of nearly 20%. Compared to that, Naruto's hentai-rate is only bit more than 18%.
Of course it has to be considered that To-LOVE-Ru with its ecchi-elements makes for better material for hentai doujins and the hentai-rate is thus higher, but I think this still proves that the manga is quite popular.

But more importantly: If To-LOVE-Ru wasn't popular, Weekly Shonen Jump wouldn't let it continue.

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yeah. i really like the series and the doujins are well done.
with 132 chapters (i think) the fanbase has gotta be relatively large for this series to be going on this long.