I opted for the one-click manual download first, just to make sure it works. Glad I did.
This plugin has a well-planned interface, and the incremental progress indicators are a nice touch. But functionality over form is key for a utility such as this.
The last progress indicator I received said the backup file was complete, the red information block above changed from "don't navigate away" To "backup complete". But when I clicked on the "Download backup" link it said I had no backups.
So I tried it again, this time waiting a little longer, same result.
I'm running WP 3.2.1 (I'm attempting to do a backup prior to upgrading to WP3.3.1, that's why I'm still on 3.2.1), Linux server, PHP 5.2+