if load sof people logged on then server will slow down. It may need upgrade to new server but this costs money but i'd imagine with the adverts on here they are making plaenty to upgrade. I am a member of a forum online and there are thousands of member but they dont allow advertising so members pay 10 quid subscription to use it. Well worth the money if ye ask me. It was meant to be yearly but they had that many members they gave 2 years membership and also donate money to charity and other things. it is totally non profit making and site runs great.
I wouldn't pay to use this site though as advertising on this would more than pay for running server.