Google seems to be giving article directory pages less and less power in recent times. It's no longer the easy ride to the top that it used to be.
There's no easy answer for a question like "how many". It might even be none at all, depending on what sites you submit to. Or it might be one or two will go to work for you, but then the power starts to fall away quite quickly after that in most cases.
The bottom line is that Google is not looking for links that you can placeon your own power. Google is looking for links that others place to you, freely given without any payment. Those are the links that will continue to work for you into the future.
I often see articles I've submitted ranking well on G so all the time this is happening I will keep using them. If G devalues the importance of these so what I'll still get the traffic from them and maybe a little link benefit - its still a lot more productive than trying to work out link exchanges with some webmasters that still a link within a resources section is a quality exchange