I had to close it down because the workload became unsustainable pretty quickly (i was running another startup at the time).
My advice would be that you know your content generation strategy very well and make it work in such a way that you don't get burnt out.
I would also suggest that you offer an incentive on signing up. People don't normally like to sign up to newsletters that are just newsletters. I offered to plant a tree for every person that signed up (cost was only $1, i would earn double that from ad revenue in a year and that's when the trees would be planted.). It worked really well, i had an almost 30% conversion rate.
Also do as many things as you can to get people through the door and establish momentum. No other business needs more momentum to build than email newsletters. Word of mouth is king.
Hope that helps.