I agree with MR, many a new member (I call them drive-by posters) joins the site, starts a GB within days of joining and disappears, never to be seen again. Auto-fail mode activated.
I also tend to be very cynical. Most of the time when I see person starting a GB, you'd have to be blind not to read between the lines; They are basically saying, "Hey, I just bought this hot, new kit and am really excited about it. I'm starting a GB with a theme that includes my new kit. It starts yesterday and ends in a few months when I think I can finish my new kit!"
We all know you're going to start that kit whether there's a GB going or not and just want some virtual slap on the back (GB badge) for doing so. You're better off doing a WIP thread so folks can see your work in one thread and not have it buried between the genre forum and the GB forum.
The best GBs are those with a strong leader and with a good theme. Sometimes the theme can be wide (i.e. "Things that Float") and still be good other times they can be so wide that there isn't any real cohesion between entries.
These are just my personal opinions. I've been here for a little while, almost 10 years now, and I've seen a few members come and go since then.