cashcow,
Make it look natural. Bursts of many links from press releases, RSS feeds, and things like that are all natural. Google does not penalize this. A sudden influx of backlinks from 100 new blogs all created within a single day is not natural. This goes for blog comments and forum comments. So use common sense.
As to social bookmarking, I would dripfeed a small handful each day at different times.
Also, study the top ranking sites in your niche and see what their backlinks and backlinking habits look like. That's where you get info for getting to the top and staying there for the long haul.
There are free tools all over the Internet to do this with. Google "backlink analyzer" and other similar phrases, then fiddle with different programs to see which work best for you.