Facebook advertising is hard, and you need to be really good at it in order for it to work well. You need to find a profitable campaign, and you need to spark the facebook surfer's interest with good picture and good ad writing. If you do it right, it can pay off well in the end, but you could also see yourself loosing a lot of money as well. It's just like Adwords in a sense, but with different techniques.
Depends on the niche entirely. If you try and do the typical niches like Sex, Love, Relationships, Making Money, Gambling etc then the compeititon is high.
The above two answers basically summed it up. It's not up to where you promote, but how you do it. Every place you promote should be treated individually, as your target audience varies a lot.
When it comes to Facebook, be careful with your advertising. I have found it is best to promote Facebook pages and internal Facebook links versus anything external.
You can try facebook. But you have to buy Ads there to get lots of visitors to your product. The other solution for this can be organic traffic source.
You're probably not targeting the right audience. You need to optimize your campaigns, and spend quite a budget until your ppc lowers. Paying 0.77 for one visitor is simply a waste when promoting Clickbank products. Here's something you can do. Build an app. on facebook and start building a list or simply make an opt-in page on your website to collect some leads ...at least. Don't just waste your budget on direct linking. You'll be amazed to see the overall conversion rate with 1000 - 2000 subscribers. (of course if you're targeting the right audience) Combine Facebook Advertising with Adwords and try to scale up your campaign/ test several keywords and so on.
I liked and agreed with your suggestion. If you can't get sales right now you might get some subscribers for future promotions if you have a landing page and an opt in form. Different people might be interested in different types of product.
With facebook you can target people based on their interests, age,geographic area. So it would be better for some particular products to be promoted on facebook. With google adwords you get even larger audience with targeted interests but you cannot target them based on the age. Other than this there is no reason why facebook is better to promote clickbank products.