Well, I finally have entered uncharted waters (for me); surpassing my first Assassin's level (56) and now hitting 60.
I haven't done much (as in any) PvP yet...so I can't comment on Impeede Life. I have done a bit of PvE however (Ran through 6 villas...for some reason it let me do the "Collect lady such-and-so's belongings" twice, plus finally did Villa Pateaus (can you tell I suck at remembering names?). Dinging at 59, I had 4/5 in Lotus Weapons and Flurry of Blows, so the 2 feat points for hitting 60 meant I could either cap them both off but get nothing new (boring!) or cap one off and put one point in the next thing.
I chose Lotus Weapon->Swift Ending. I love it. Again, haven't seen the effect on PvP yet but it's awsome PvE. Okay, so it's not *that* big of a deal for PvE, but those times where your second combo doesn't quite finish the mob off, they seem to die now.
The tool-tip says it increases the damage of your Flesh Rot and lotus weapons procs, and that it further increases them as the target nears death. I don't have any numbers yet...I'll have to check on the official forums. I don't know if additional points increases the increased damage, or if it's just "filler" to make you spend points to get the next teir's feat. We'll see.