The board of Yahoo has, for some reason, decided that it is in the companys best interest not to take the offer. This is their judgement. What I'm attacking is that they are being sued because of their judgement. And the reason you pick a board of directors in the first place is to exercise judgement.
And if the board is constantly being sued whenever they make a move that is not entirely predictable and not in any way offending to anyone they don't make judgements based on the companys best interest, but based on their fears of repercussion through legal action.
I see your point that if you are a minority investor there is not much you can do if you don't believe in the boards decisions - but then you should sell your stock.
Just my opionion :-)
Oh - and welcome to YC news, hope you like it.