My experience:
DFB -
old and well indexed website - yes! Give it a week or so to gel, and you should see some nice results. This is, of course, not my only linking method. But it is my only
new linking method.
new and not well indexed - no harm, no foul. I am not seeing much in a hurry - so as advised, they also need other types of links. And franky, they just need to age a bit for competitive keywords.
That said, I have a fairly new keyword domain that has been steady on page 1 after I had the domain about 3 weeks - but I can't budge it above the fold. I only pointed DFB at the web 2.0 - and am hesitating to point it at the actual website. I am getting closer to stop being a big chicken, but am just not there yet.
web 2.0 - takes a while, but yes. Again, give it a week or so to gel (i..e let SE's find your links)
But i have been very conservative. i.e. spreading links around. This has, I am sure, been diluting the effectiveness.
I was scared to point this at money sites because I'd had a bad experience with a huge blast somebody had run before .(Even that ding was temporary.) BUT these are small - 500 at a time, which will not all get indexed the same day - so it isn't so risky - IMO.
Also, I see that the other SE's are kicking in a lot more. So in addition to qualified success with G, it has been (IMO) encouraging more traffic from the other guys. In some of my niches, Bing and Yahoo are actually better sources of conversions.
p.s. I haven't been pinging, but I'm getting aruond to it.

I am sure that would speed things up. Why have'nt I been pinging? Just haven't. Some questions have no logical answers.
Anyway Do your own testing. It's cheap.