If you're in the current YC class, you should know there are more effective options for you to do your hiring plugs than polluting other threads.
You are right - there are more effective options. However we're at the stage where we'll take whatever chance we'll get to spread the word. As a small startup with limited resources you have to stay hungry.
It's definitely not out of line to plug that you're hiring-- my point was that you would be better to avail yourself of the special "hiring for YC company" posts built into the system, and I see that you've done exactly that.