It is not terrible.
Dallas is rumored to offer Stackhouse in a package for Artest.
But I think the team is still better with Ray at SG and Pierce at SF vs. Pierce at SG and Howard at SF.
And there in lies the problem of the trade. I think when some people propose trades 2 for 1 trades, some part of their subconscious looks at the deal and thinks that the two players coming to the Celtics can both play the departing player's position at the same time. But as wdleehi points out, it's really about how it translates to floor time.
As much as I've complained about Posey leaving, assuming that Pierce and Allen can stay healthy and out of foul trouble in games, it should be a fairly easy problem to mask in the playoffs because both Allen and Pierce can play 40 mpg. Thus, we're only left with a collective 16 mpg (this is playoffs, not regular season), to account for backing up the 2/3. Thus, as wdleehi insinuates, is it worth having a decline in production for 40 mpg to have an improvement of production at the backup 2/3 for 16 mpg? I don't think so.
Trading stars for a bunch of good players never works out in the NBA. Just ask the Sixers about the Chamberlain and Barkley deals.