They can become very massive, are very friendly, a tad ehm....'goofy' or perhaps 'simpletons' (at least the few my mother imported from Norway).
The first one my mother took home (by plane :-)) got run over by a car quite soon (IIRC he didn't live to become one year of age). The second my mother imported had more success (she still lives) and had a litter here, among those kittens a few have grown to gigantic sizes. My parents' neighbours have the most colossal one. My brother emigrated to Norway some 2 years ago and he took one of the offspring of the cat my mother took from Norway back to Norway :crazy:.
Here's a pic of the 2nd one my mum imported, quite large when compared to the cute little black one :-). Though this cat (Sylvi) isn't that big when compared to 'proper' forestcats. I think it's a halfbreed.