And this is what it looks like.  Hit the bevel button to add the bevel, and change the value in the box to change the size (there's a slider too, but I don't really find it very useful).  I'd avoid the recursive button (that makes bevels on your new beveled edges so it's more rounded), I've had some really bizarre stuff happen on more complicated models and you probably don't need it.  It's more stable now than it used to be, though, so maybe that's fixed too.

Edit: I just noticed you can change the start and end points of the slider--did that used to be there?  That might actually make it more usable...