Shield swipe does not add dps anymore. Despite its buff, the damage of shield swipe is less than the average dps of the goring blade (without dot) or royal authority combo. Given it costs a gcd, if you want damage you are better off just doing your royal authority combo and ignoring the proc. The threat gain seems to (according to blue garter testing) not be very much--an extra savage blade or so. The gain in dps was good compared to the rage of halone combo, but only barely. The saving in tp is also very slight (about 10 tp recovered per shield swipe).

In general, shield swipe is a trap for paladins that don't understand the mechanics of the class or, rarely, need more aggro (but realistically, this is almost never a concern outside the first few moments of a fight or right after a tank swap).