Weeden got a bit of a raw deal. He gave us our best 4 quarters of QB play all year (how sad is that) in his first four quarters as a starter. Who knows how that Saints game might have turned out for him had we gotten he ball first. He had no Dez, and he had a lot less defensive support. I don't believe for a second NE wouldn't have made Cassel (or any backup we might realistically have had at that point) look just as bad in that game. And then that was it.
That said, he really didn't have what it takes to be anything more than an average/below average backup. And he's too old to develop, so it doesn't really matter.
Cassel is another story. He obviously needed a little time to get comfortable with the offense, but he showed signs of being able to move the ball in the NY and PHI games. He's regressed awfully, though, the last two weeks, to a point where, in my opinion, he's not serviceable. I don't know what it is, but he can't move the ball downfield anymore, and he's inaccurate even on the check down passes. And it's horribly boring to watch.
I'd be playing Moore from this point on if it were my call.