[logn]

Welcome to HN.

Upvotes suffice and moves the response to the top, letting everyone know it's the favored comment. 'this' will get you negative karma eventually.

[bennyg]

I don't know, another comment echoing the same thing is like two people talking to you. An upvote doesn't hold the same weight psychologically (at least to me). Maybe more could be said than "this", but that's just me.