I tried (in my development server), but the /user/portait/upload-2 TCL script says...
We had a problem with your input:
* Your image wasn't one of the acceptable MIME types: image/gif image/jpeg
but, ok, I got the idea... so I added "image/png" in "AcceptablePortraitMIMETypes" in the "User info" section and it works!
Thanks!
My first message was because even this site doesn't allow uploading png files as user portrait. May be it could be nice to check that feature for the new OpenACS release, in order to add that default value to the "AcceptablePortraitMIMETypes" parameter.