I think it's getting very exciting. For long it seemed that Sony was definitely going to beat MS but now it isn't that certain anymore. I'd still lean more towards Sony, though.
Nintendo is a very different case, however. I believe Sony might have a chance to challenge them, but that's just might, not will. Sony might be able to challenge them only if they beat MS early enough. MS on the other hand, has no chance against Nintendo even if they win Sony (unless they can somehow change their image which would be a small miracle at this point).
Please note that I'm not implying Sony will be able to challenge Nintendo; I'm only saying they might have a chance if everything goes well for them.