Received this e-mail today; it seems like Bittrex is working on something new:
These credits are going to be adjusted in the trade fee. I've got $25 worth of free credits (2500 credits); so it makes 1 credit = 1 cent. Going to try this out and let y'all know my experience!

After credits, we may be getting another exciting feature. I just logged in at Bittrex and found this new notification:
How are the credits coming along? Did you spend any?
I can say that for the one or two regular posters in this thread complaining, Bittrex does have a good reputation and seem to be innovating as with their credits feature.