OK, it's no secret that Charms do shoots with each other, sometimes groups depending who knows who, locations, schedules, and so on.
But if I may be so bold as to make a request? When you do a shoot where you're a guest on another girl's site, post a link to it on your own site. With an average of 800 Charms at any given time, it's impossible to check every girl's site every single day to see if your favorites are making a guest appearance somewhere else. Maybe some of us would be willing to join another girl's site if we knew that one of our favorites guested over there from time to time.
Part of what makes the Internet what it is is all the cross linking among sites with related content or that expand on something from one site to the next. Use it to your advantage.