I've had quite a bit of success promoting my services on Facebook. Here's how I did it...
First I joined many social networks and forums in my niche and got to know people there. Then I added them all as friends on my facebook account.
I found that very quickly facebook was suggesting other friends of friends that were also interested in my niche. I reasoned that if I shared say 4 or 5 mutual friends then I would add them as they are very likely to share my interest. You can also check some peoples profiles to see their interests.
I also gave my facebook address on my site. What I have now is around 1,300 friends, and growing, that are all interested in my niche. Now I'm finding that people are looking for me, or finding me through friends of friends.
You can also join groups that are related to almost anything on facebook - these can also help drive more targeted friends.
Also if I see a site or blog I like, I will sometimes try and find the owner on facebook and add them as a friend.
I suppose the real trick is not to just go for quantity. If you do you will just have loads of spammers and other deviants that are not interested in your products, and may actually try and do you harm. And this will probably attract other spammers and deviants.
Keep your friends 'pure', and you will likely attract more 'pure' friends that are interested in what yo have to say.