I've been doing it for quite sometime, probably about a year.. On a scale from 1-10 (10 being most painful), i think its about 5? Painful in a sense that well, you're plucking hair out. So of course it'll be painful..
On the hindsight, they pluck a few hairs together at the same time, so it's more like a "pain-but-get-it-over-and-done-with-pain".
I go Bishan for the eyebrow and upperlip threading. It's $5 per area. I would say, threading is much neater than self-plucking. And they shape the eyebrows beautifully, so no worries on the shape.
And I recommend the place I go to. It's a small shop, on lvl 2.. PM me if you're interested (then i'll go find out the name of the place!) LOL. Nv really notice the name of the place, cause my colleague brought me there.