I have been on the fence about this for a while, im a firm believer in you have like 5 to 10 seconds to get someone who is visiting your sites interest before they click out and leave. now here are my thought on good and bad with using a slash screen which requires a join to view site content
the good
lower server load with mass index page hits, due to a simple page being loaded
cleaner look with less clutter
fast load times
adding privacy to the site
lets the site look more "professional"
the bad
less stuff to grab someone interest at first site
people thinking "man i dont want to go through a long joining process just to find out i dont like it"
people thinking "it says joining is FREE, but nothing is ever FREE"
people leaving before they see all the options your site has to offer
.. just trying to get other people views on this thought