Steam wallet balance is now once again a flat $0.00. It was something like $0.34 awhile back. My first guess right now would be that it was used in a recent Steam purchase. I certainly hope that's the case, and will test it later next time I buy a game by depositing some cash first.
I'd go cross-check it, but $0.34 is what I keep lying around here and there in hidden spots around the house, and I CBA to dig that out either.