I ran a whole bunch of calculations between the standard 401(k) and the Roth 401(k), before ultimately deciding to put the whole kitten caboodle, 15% of my paycheck, into the Roth option. (You can see an earlier posting for more information on my Roth decision.)
I called Fidelity a few weeks ago and last Friday my paycheck showed the difference between the before and after tax options. A total of $183.57 less.
The Roth 401(k) is about five kinds of awesome. Glad to hear that your workplace has picked it up! I think a lot of places are hesitant because the legislation is expiring again in a few years.