Blake would be a good stop-gap measure until either Middlebrooks is ready or the team decides it needs to go in a different direction (if Middlebrooks takes a step back.) They also need to figure out whether Lavarnway's defensive skills are sufficient to consider him a viable backup next year. From what I have read, he is pretty limited defensively so he is likely a DH. That being the case, I wouldn't mind seeing the Sox add a solid defensive catcher to the mix. Not sure if Yorvitt Torrealba could be had from Texas but I'm sure there are others. I think Salty showed enough signs of life to be in the mix but I don't think you want him catching as many games as Tek did a few years ago.
Note that in order for my trade to work, the Dodgers would have to pick up Blake's option for 2012, which, I see them doing if for nothing more than insurance.
I've heard a lot about Lavarnway's defense not being great, but every time I've seen him play (whether in Pawtucket or with the big club) he doesn't seem all that bad. I mean, Lavarnway threw out something like 30% of runners last year, so at least that aspect of his defensive game is better than what we've seen from Red Sox catchers over the past few years.