I've only been on my SV for about six weeks, so I'm probably one of those new members the OP is referring to.
I did a bit of research and the general opinion seem to be that the SV is a great first bike. That probably explains the steady stream of potential. members.
Retaining new members depends on the nature of the forums. The folks on here seem reasonably civilized and they are more interested in biking than calling each other names. Plus, the moderators seem to be doing a good job of keeping the trolls and spammers at bay.
That's pretty much what I'm looking for, decent people and a good signal to noise ratio. So I reckon I'll be here for a while, and hopefully make it up to Frith St. again before too long.
Just my thoughts,
Keith.