I think Red Sox fans overestimate Bronson Arroyo's ability. This is in part because Arroyo was named after Charles Bronson and has brass balls (he was the guy who hit A-Rod and set off Varitek's "smell the glove" response). Red Sox fans love Arroyo like the previous generation of Sox fans loved Bernie Carbo. And like Carbo - Sox fans greatly over-value his talent.
Let me first say that I would be strongly in favor of a Red Sox trade that involved Arroyo to the Mariners for Jeremy Reed (or an Arroyo to the Rangers for Brad Wilkerson trade). The U.S.S. Mariner pretty much hits the nail on the head with this evaluation of Arroyo. Their conclusion may not be welcome news to Sox fans but it is correct:
If the M's are determined to have a veteran pitch-to-contact innings sponge at the back of the rotation, Arroyo isn't even superior to Jason Johnson. Johnson, a free agent, is basically a groundball version of Arroyo. Throws strikes, doesn't miss bats, but induces groundballs instead of flyballs. Oh, and he doesn't cost us Jeremy Reed.