Can anyone tell me what to expect when a product does well on ProductHunt?

Did you experience a significant increase in paying customers?

Not in my case, because when I launched IH on PH, it was a free product for consumers. But it did lead to lots of mailing list subscribers, which is what I was optimizing for. I think you have to choose your own metric. Whether or not you'll do well on that metric depends on…

• whether or not the PH audience of techies and makers is what's right for your product
• how optimized your site is to actually convert people once they arrive

Both of these are things you should think about before launching on PH, not afterwards.

What kind of publicity did it generate for you?

I got #1, which resulted in something like 7,000 unique visitors over the course of a Sunday and a Monday in August 2016.

Is PH a good predictor of product success in the long term?

PH is a single injection of traffic. Unless you have a product with a viral coefficient > 1 (and almost nobody does), that traffic is going to peter out and go away, and you're going to have to find another more sustainable way to grow for the long term. The same is true of any other press or launch event. For most companies, growth is a grind.