I have an iPhone 5S 64GB with 10GB free, and an iPad Mini with Retina 64GB with about 8GB free, and both ran into the stalled progress bar issue, the iPhone at 40%, the iPad at 69%. Doing a forced reset as described here by modular747 rebooted both and got me back into my lock screens, with installed versions showing 7.1.2.
As one poster here mentioned, it's possible this stall on the progress bar may have been related to the encryption of mail attachments running after the update. Someone also mentioned the mail bug was still there after the update. Were you referring to the encryption bug, and if so, how did you test for it?
I will be reporting this to Apple to have them look into it, as it's definitely not normal for a stall like this to occur.