Good job mate. Text placed over the top of that 50% coverage might be a little difficult to read though.
There are a few WPS's that use this type of design element, but to do it properly, they pre-blur the background eg in the actual background image itself, thereby achieving the effect but limiting you to using the same background image. One example of this is the Jclix series of themes.
For what it's worth, I knew what you meant by transparency.