from my experience there are a few rare times when i would use Lethal Resolve over Blade Frenzy. times such as these would be if you are in a group and there is no tank (hopefully a couple healers) and u get the job of tanking/pulling. as long as there are more dps folks in your group, Lethal Resolve will help out your healers just that much more.
other than that, i find Blade Frenzy to be much superior b/c when u switch on LR, u lose attacke benefits from your base #. with BF, u gain attack benefits from your base #. subtract LR # from the BF # and you will have 50+ attack difference. that's huge in light of the dps difference which when soloing or small grouping (especially when you're the one taking hits) the BF added damage will benefit much more by finishing the mob sooner than holding out on the defense. remember, we're offensive chars and don't have a whole lot to offer on the defensive side.
my 2cp anyway.