It is very likely that all members have been on another forum first before they joined here.
So the question begs, what are these other sites you visit?

There is two other forum sites I go to (well, three if you include DeviantART, but I never go on their forums), & they are;

ONM; http://www.officialnintendomagazine.co.uk/

The SEGA boards; http://forums.sega.com/index.php

Same as you, only I vist this forum sometimes too http://www.spyroforum.com/

You wanna list?

Marriland

AnimeForumX

Roleplaying.PlanetMudkipz

ONM

.hack//New World

The World {enter the game}

Roliana

Mugglenet

Spriters Resource forum

Pokecommunity

Pokemon Acanthinite forums

DeviantArt


That's about it, I think... I'll update if I remember any more ^^