It can but only if many people bookmark your site and say it makes it to the popular links page of a major site such as del.icio.us.
Yes, there are plenty of Social bookmarking sites that will give you a ton of trafic. Try it out for yourself.
yeah it increases traffic if your link gets maximum bookmarking and if your links get in top listing in main page
Social bookmarking sites should not be relied upon as traffic building tools, but rather link building tools. The traffic is almost always fleeting, non-targeted, and thus non-converting, meaning you're not going to see any noticeable conversions, sales, etc. from this traffic. Assuming you're giving this traffic a reason to link back to your site, they typically will, and you can see hundreds, even thousands of inbound links to your site pop up within a few days or weeks.