In the beginning of the web era, Haaretz still commissioned academic Judaica articles before every Jewish holiday. They made great printouts to take to shul.
In 2002, Yosef Yahalom wrote a concise article showing that the piyyut is originally a conclusion to a piyyut by Yannai later attached to Kalir and was not written by R. Amnon in Ashkenaz.
The piyyut, or sacred poem, “Unetaneh tokef kedushat hayom” (“Let us recount the power of the holiness of this day”), is one of the central and most thrilling texts in the liturgy of the High Holy Days.
This text was written by Yanai’s most celebrated student, Elazar Hakalir.
A year later Hananel Mack wrote a follow up article, less certain which Byzantium author wrote the poet. But Mack shows that the vision of the angels themselves being judged is a theme of Kedusha, so the piyyut was originally a ending poem to a kedushah piyyut.
Additional corroboration for the claim that the liturgical poem `Unetaneh Tokef’ was written during the period of Yanai and Elazar Hakalir and not, as tradition says, by Rabbi Amnon of Mainz.
However, here we hear for the first time of the fate shared by heavenly beings and humans, who are all judged on Judgment Day – that is, on Rosh Hashanah and, apparently, also on Yom Kippur, which is also a judgment day and is also mentioned in the body of the piyyut.
This topic is a reminder that we do not have a good book on the theology of Judiasm 600-1100, the great age of Piyyut and Aggadic Midrash.
Update 2010- Haaretz is no longer giving free access to the articles.
The Book of Doctrines and Opinions: 
Yahalom argues that unetaneh tokef is the siluk of a piyut by yannai, not kalir. what we have now, represents it after it was detached and re-attached to a kedushta piyut of kalir, the siluk of which went missing until recently.