Did you spend a lot of time to raise your Badass ranking in
Borderlands 2? You might want to hold off on downloading the Mechromancer DLC. That is if you want to keep your Badass ranking.
There are reports that some folks that have downloaded the DLC has lost their progress as well as golden keys. Ouchie! It doesn't seem to affect everyone, but this bug's cropping up on a few folks and it's one that can really be aggravating if it should happen to you.
The bug seems to be platform independent. The extent of the bug is still being investigated, but I hope those affected are able to get their ranks back. Until Gearbox can nail down what's causing this, you should probably wait to install it.