Jacko, the optimism is not necessarily with the rotation itself, per se, but with the overall team. You can't look at the rotation in a vacuum. This rotation is not going to set the world on fire and it leaves a lot of people thinking "meh". However, when you consider several other factors, there is reason to be optimistic that it will be good enough to keep the team in contention, at least until the Sox can add another starter.
As far as optimism for the rotation itself, there are reasons to be hopeful that these guys can show improvement this year. Buccholz is a flip of the coin, but when he's good, he's very good.