Tis is OS X 10.7.1 and PM 4.6.8
It has been discussed before that deleting files out of PM is slow, not it is even slower and the Finder's "Moving XXXX items to Trash" dialog pops up twice. The first time it's fast, then, after a maybe 1/2 second it pops up and stays there for a long time (last time I deleted 800-something NEFs, 1700 files all in al and it took minutes). Finder is completely blocked with a spinning beach ball.
Bridge 4.x takes about 5 seconds to delete 1600 NEFs with the finder not getting blocked at all.