I went to two French conventions only ("Cartoonist", in Paris and Toulon, in 2002)
It was about Manga, Anime, and cosplay.
It was more an excuse about meeting with IRC friends from all around France than seeing the convention.
I would have liked to go to Frankfurt, Germany, in 7th & 8th July 2012, for
Cosday convention.
But I don't understand nor speak German at all, and alone I don't feel at ease in an unknown place.
The website is in german to order tickets too

So I won't go.
The real reason I would like to go there is not for the convention or the copslay itself, but to meet with two persons from Youtube
Violintay and
Lara (their
piano/violin duo on Morrowind/Skyrim theme)
Taylor is American, and Lara Australian. They will meet their fans at this convention.
Going to the convention only to see them is kind of weird, there would be a lot of fan/groupies around them all the time. I wouldn't stay with her for two days long, we don't really know each other (we only wrote PM to eachother). Or I'll take my violin too? I'm not as good.