The post_id can have several different types of values:
- The special value of 0 (zero) or "last" corresponds to the last post you have made (status update, wallpost, feed story, etc.)
- The special value of "curstatus" corresponds to the last status update you made.
- The post # from the last STREAM or FSTREAM command. This requires that the stream_save preference is set.
- A full facebook post_id. This can be seen with the stream_show_postid preference. They are typically very big numbers that look like "1234567890_ 1234567890"