I have a couple of items that pop up as I continue to think about the Jerusalem Council.
1. If it is a historical event (which I lean toward because of the knowledge and application of the Noahide laws in early Christianity; and we would expect the Jerusalem Church to be the one who "ruled" on the Gentiles), then it likely occurred after the Antiochean Affair, not before.
2. It does not have to be identified with Gal. 2. This could be an entirely separate affair. Gal. 2 may be an earlier meeting. Paul may not have even been involved in the Jerusalem Council since its food rulings are no compromise for Paul. It is not clear to me that the Jerusalem Council made any decision about circumcision (see Acts 21:25).
3. For years (even from the beginning?) the Jerusalem Church allowed for a range of behaviors on the part of Gentile converts, and supported the Antiochean Church (and at first Paul) which allowed Gentiles to remain uncircumcised, but not Jews. Peter was the big advocate for this position, and this moderate position appears to have been permitted by Jerusalem who sends Barnabas and other teachers and prophets to help with the Gentile mission. The Gentiles in Antioch weren't necessarily circumcising themselves given Paul's connection to their mission.
4. There seems, however, to have been real hostility especially in Jerusalem in terms of Gentiles who remained uncircumcised, perhaps for fear that the implications would be that Jews don't need to be circumcised either (if we follow what Luke tells us). Here I'm not even thinking of folks within the Jerusalem Church. I'm thinking of Jews external to it. Was Stephen's martyrdom about it (cf. Acts 7:51)? Was Saul's persecution of the church about it? Was James son of Zebedee killed by Herod because of it? Was Peter arrested because of it? Was the riot that got Paul arrested because of it?
5. Something happened in Jerusalem in the 50s that caused James to send an envoy to Antioch telling them to circumcise the Gentiles. This doesn't have to be a case where James is going back on his word. This suggests that something socially or politically was happening that caused James to finally make a decision to circumcise the Gentiles, a decision that he maintains following the Antiochean Affair when Paul goes out on his own and faces churches who are now being told by Jerusalem to circumcise the Gentiles. In other words, the uncircumcised had become a liability and James had to act. But why?
6. After the Antiochean Affair, James rules on the food laws, and allows for Gentiles to follow some form of the Noahide Laws. Is this later ruling the Jerusalem Council?
UPDATE 10-10-07: Doug Chaplin posts his thoughts on the subject here.