And what about the ePub vs Mobi War?

I mean, some say the mobi is an outdated eBook format, and that the ePub allows better formatting and better eBook look, so your opinion?
And btw I wonder why the Kindle is heavier than the Kobo or the Odyssey. It looks like metal but the Kindle is in plastic, right? And same size... perhaps a bigger and heavier battery?
Oh and I have read a customer review which say we cannot download more than one dictionary, and so we have to choose. Is it true? I would like a french dictionary if I read a french book, an english one if I read an english book, and translation dictionaries as well. We cannot have all this together?