So I was lucky enough to get 2x egg sacs from 2x females late last year (females courtesy Noob and Shinobi Dragon).. a champion male was waiting to do the honours and survived both to tell the tale (matings 13th Oct and 11th Nov). Having never bred spiders before I couldn't contain my curiosity for long and pulled the 1st sac at 6 weeks. I opened it a little just to check what was happening, got a peek at lots of spiderlings then put it straight back with the mother. 3 days later they emerged from the sac on their own accord and I then removed them for the final stage away from the mother. 79 viable slings in total.

The 2nd sac I decided to leave with the mother to full term. She opened the egg sac herself a week ago and they swarmed out pre-molt. Perhaps of interest for those of you that pull sacs early, all the spiderlings moved to the top and sides of the funnel, out of harms way of the female and her sac rolling. They started molting out on Monday, exactly 3 months to the day that the female mated. I pulled 50 last night and then ran out of tubs. There looks to be another 100 or so at least still in the hide (see pic of hide entrance). Also of interest is that when I removed the female from the hide last night, she was only concerned with protecting the empty egg sac and made no attempt to stick around in the hide with the slings.

So in conclusion and after some very limited experience, I can thoroughly recommend leaving the sac with mom to full term - what a pleasure.

UPDATE 18/02/13 : 203 viable slings from 2nd sac.

Hehe it's still a matter of preference. Friend of mine pulled his gbb sac at 2 weeks middle of jan and incubated further himself, and he's sitting with 229 premolt 1st instars now..
Awesome picture!! they are the cutest slings!!