After reading http://lists.wikimedia.org/pipermail/commons-l/2012-August/006641.html I thought I'd try it out on http://mwreview.wmflabs.org/wiki/index.php/Special:UploadWizard.
I tried uploading this photo: http://www.flickr.com/photos/craftybunny/88011957/
It goes into an infinite "Uploading..." for me[1].
No console errors.
Trying again when checking for HTTP requests I see a POST request to api.php with response {"options":"success"}. Though there is a response indeed, the request itself is marked as "Aborted / Cancelled" in the "Resources" tab of the Development Tools in Chrome.
Not sure what's going on, but it appears to be a logic problem (a missing error handler somewhere, causing state to get stuck eventhough the asynchronous action did in fact get back, just not with success) - aside from the fact that the api.php returns in error, which is another problem.
[1] Left it open for 20 minutes, this is not a slow thing or a time out. Polling resources, http requests and console messages, it seems like it died very early on (1-5 seconds in) and nothing happened after that.
Version: master
Severity: blocker