you need a lot of backlinks to promote your site and to make it rank in Google. It also depends on the keywords your using. the more competitive the more quality backlinks you need.

It's not just backlinking would help you to market your site, you need to have also good content in your website and optimize your keywords to perform better in SERPs.

I agree with Bob. Concentrate on providing a useful and meaningful destination and the 'backlinks' will take care of themselves. Promoting your site in the search engines is obtained through keyword research, good URL naming conventions, optimized title, meta and alt tags, sound coding, and quality content.

100% agree..promoting your sites does not depends on backlinks, it's on the content because even though your site has a lot of backlinks but not high quality and informative content it is still useless and you will not earn bunch of money

Last thing is most important and then your backlinks take care of yourself for sure If you can't write content yourself, hire someone (professional)

A sudden growth in the number of apparently independent peers, incoming and/or outgoing, with a large number of links to individual documents may indicate a potentially synthetic web graph, which is an indicator of an attempt to spam. Request as many links as you want keeping in mind many will ignore your request. Again, link building success or failure is going to to depend mostly on what other webmasters think of your site which is why link building and content updates go hand in hand.

You'll need some links, but the number will depend.
If the cuality of the links is really good, like PR5 or even more, the websites are related and have a good position in google, you'll provably need 5 or 6. But only if you have a good site, with unique and interesting content.
If the links are in bannerfarms, link sites, free directorie,s etc, then you'll need LOTS

I think it all depend on which keywords you chose and if they are competitive or not. More competitive keywords might need more backlinks and more time to rank better.

Backlinks are not the be all and end all of ranking for keywords and neither is PageRank. Every website owner wants to rank in Top 10 on Google and the big G takes into consideration many parameters, including domain name, keywords in URL, Meta tags, CONTENT, age of website, number of years that the domain and hosting has been registered for, subdomains, site structure, page names, site design, back links (quality is important), etc.