I am having the same problem that other users have posted in the discussion thread. The error in IE8 is "Expected Hexadecimal digit" in FireFox 3.6.1 I get an error that the file can't be uploaded.
The Domino server log shows the following even though I have set the configuration to local files (not Amazon S3) and restarted HTTP.
01/28/2011 09:09:09 AM HTTP JVM: DOJOX.Form.FileUpload To Amazon S3 : Started
01/28/2011 09:09:09 AM HTTP JVM: DOJOX.Form.FileUpload To Amazon S3 : Load com.amazonaws package
01/28/2011 09:09:09 AM HTTP JVM: DOJOX.Form.FileUpload To Amazon S3 : get Access To The Uploaded File
01/28/2011 09:09:09 AM HTTP JVM: DOJOX.Form.FileUpload To Amazon S3 : Upload Key : uwye4g1ur85c
01/28/2011 09:09:09 AM HTTP JVM: DOJOX.Form.FileUpload To Amazon S3 : Upload Days : 14
01/28/2011 09:09:09 AM HTTP JVM: DOJOX.Form.FileUpload To Amazon S3 : Temporary File Name : LICENSE.txt
01/28/2011 09:09:09 AM HTTP JVM: DOJOX.Form.FileUpload To Amazon S3 : Corrected File Name : C:\DOCUME~1\NOTESA~1\LOCALS~1\Temp\notes57DA2F\xspupload\LICENSE.txt