I've noticed today that Duane at Abnormal Interests has also shared some thoughts on the Gedalyahu seal. I think he summarizes the significance of the find well when he says:
"Does this prove the Hebrew Bible in some way? No, not in the way that some might hope. It does seem to confirm that a person named Gedalyahu likely lived at about the time the Hebrew Bible indicates that he did and that he may have had something like the role the Hebrew Bible says he had."
Everyone interested in the seal should also take a look at the detailed discussion by Chris Heard at Higgaion. He includes G.M. Grena's drawings of the seal along with comments on Grena's paleographic analysis. In considering the identification of the character, Grena comments on the post and mentions the important detail that a similar seal (the Jehucal bulla) with the name of another official mentioned in Jer. 38:1 was found earlier by the same archaeologist at the same site.
The fact that two bullae bearing the names of Zedekiah's officials from Jer. 38:1 were found by the same archaeologist at the same dig site can be taken two ways. Either they reinforce each other's connection to the biblical verse (a real find independent of the biblical text that corroborates a detail from the text), or the biblical verse suggested the connection (a questionable find dependent on the biblical text for the association). I'm not personally questioning the authenticity of the find (though seals have been forged before). I'm just pointing out that statistically, it's either the real thing linking to biblical persons or it was faked to look like it. For one antiquities dealer's description of how he sifts out the authentic artifacts from the fake ones, see here.