Well mostly the marketing for a new website happens before I buy the domain, scripts etc.
The marketing plan contains forums about the niche, so a few days before the site opens I start posting the forums. When the site is launched, I mostly have 50-100 or more posts, so I add the new website to my signature, mostly I built some rep by than which gives me more traffic
I'm not into social bookmarking, but I should check it out too I guess! I hate blog posting, just to get traffic to my own site. So what I mostly do is search for blogs in the same niche, find questions of other people in the comments or in the post, and than create a page with the answer from my site -- Than I'll post a link from the comment section to my website, that sort posting is better than just a link under my username or a post with 'Go to www.xxx.com for more' etc
Just my thing