Well, I'm glad people use "тысячей" anyway.
It's just that I saw this form in some intermediate books where it was mentioned on a side.
Also, I've just found this, where they talk about it in the lower section of the page:
http://www.gramota.ru/spravka/letters/?rub=rubric_92
That's why I kinda got confused with the inconsistency of it's use in some books - Aight - I'll stick to what you guys say then.
"тысячей" is the way to go.
Thx!