You need an invitation in order to use Sixfoo! 660, but you're probably not special enough. Sign up for the feta waiting list, then cry from the corner of the playground while the kewl kids enjoy the the foursquare court. Why not round up all your 12-sided dices and go beg for a Gmail Account, sucky baby?
Create yet another place online. Share pictures of your cat. Create a blather. Make the same lists of crap you made somewhere else last week, send out a BLAMMO, crush on an indie chick and abandon it all after only 12 days. See a confusing example.
Invite social apps to your place to see what works about their service. They can steal ideas from your service. Tag each other silly until you can't feel your toes. It's a great way to feel like something new and important might be happening before the bubble bursts again in early 2007.
Share as much as you want, with whomever you want (plus whoever can hack). You decide how easily you're stalked.