Just noticed this. The method takes parameters "user_a" and "user_b", which are the ID or screen_name of the respective users. And I just tested that the API assumes the value is an ID as long as it's numeric, so user_a=13 refers to twitter.com/biz and not twitter.com/13
Just thought I'd share with the group in case someone gets tripped by this. Yu-Shan -- “When nothing seems to help, I go look at a stonecutter hammering away at his rock perhaps a hundred times without as much as a crack showing in it. Yet at the hundred and first blow it will split in two, and I know it was not that blow that did it, but all that had gone before.” — Jacob Riis
