I think that unless you have an overall vision and reasons for running a closed beta, you should open it up. Forcing users to invite their friends for earlier access only works if your website has the capability to go viral. It's worked for the few companies who initially did it, but too many companies are jumping on this method, in my opinion.
If possible, I think the "best of both worlds" solution is to have an open beta, but encourage users to invite friends by offering something other then early access. I do this with my startup and it has helped get the word out.
If possible, I think the "best of both worlds" solution is to have an open beta, but encourage users to invite friends by offering something other then early access. I do this with my startup and it has helped get the word out.