When stickies are okay:
1. Sword coming at you, you know you're going to die. Sticky is the best way to take him out, too.
2. Any time you can stick someone without them seeing you, or from a distance. That's just plain impressive!
When stickies are lame:
When people are point blank and they stick you when you're trying to melee them. They're basically giving up and killing the both of you. I will never stick someone close range unless i'm positive i'm not gonna win.