Thanks, I suspect that my site will have rather long sessions (30 minutes?). I plan on supporting anonymous, free, and paid users. I suspect that most of the users will be anonymous and/or free (I'm considering advertising for some of these. My system will also have a higher than normal communication component (a key factor in my concern on sizing).
My guess is that I should plan for a concurrent user load of about 5%-10% of the registered users (both free and paid). Included in that range would be the unregistered anonymous users. I expect at the end of the day the actual concurrent usage will be much lower. Probably less than 1%. But I don't think the hardware costs to support 5-10 are five to ten times the cost of supporting 1% (probably a factor of 2 or 3).
My guess is that I should plan for a concurrent user load of about 5%-10% of the registered users (both free and paid). Included in that range would be the unregistered anonymous users. I expect at the end of the day the actual concurrent usage will be much lower. Probably less than 1%. But I don't think the hardware costs to support 5-10 are five to ten times the cost of supporting 1% (probably a factor of 2 or 3).