Fantastic! Works great and makes complex code much more readable. I use a 95% white background for the even tabs. It is subtle but extremely helpful. May I recommend that being added to all languages where it makes sense?
As it is now, us convert-tabs-to-space types cannot use this. Not that I'm dying for it anyway, I'm all for unnesting nested code, but it's a nice idea still.
In fact, I'm a little curious to see it, could you please post a screenshot on a webserver of how it looks there for us lazy to test it on our own systems?