But even then you wont be able to prevent all spoilers from the non-spoiler forum

Spoilers will ALWAYS come to be when talking about a game. Even the Shadows of Amn board gives loads of spoilers to a unknowing newbie. Even if you would divide the game into boards according to the Chapters you would have countless spoilers. I don't think the 'there will be too many spoilers' argument counts for that reason.

IMHO, to you guys that said 'yes' to this poll, someone (maybe even you) just may ruin this game entirely for so many people. BG2 is still a pretty popular game, so it still gets lots of newbies. You really have to consider how much of the game you are willing to ruin for someone just to merge 2 forums into one. I remember reading a huge ToB spoiler about the final boss of ToB in a question I posted when:
1. My thread was unrelated to that subject.
2. There was no spoiler tag.

This ruined the game for me. I hope it doesn't happen to anyone else.

So Dundee what`s it going to be?

I think it's not. Dundee made a reply on the BG2 board. And the votes say no as well. I realize that if you check the results, "Yes" has more, but read the replies and see how many people changed their vote. Not only that, but if they were to merge, Ziroc would have mentioned it in his little update in the GD board.
At least, that's my take on things.

It's hard to say yes or no on this poll. Sure, merging the two would save space and having to jump between the two forums but post titles involving ToB might contain plot spoilers for SoA (e.g posts about a certain ToB exclusive NPC...)