Strategery - The NYTimes notes some very important political factors in amending the Constitution:

1. Percentage of amendments introduced in Congress which pass 2/3rds of both houses: about 0.003%.
2. Percentage of congressionally-approved amendments which pass 3/4ths of the states: 81.82%.

Translation: the Hill is where we draw the line in the sand. Another reason to be thankful for an evenly divided Congress, because we sure as hell can't trust our representatives to vote their consciences on this issue.