a. "What are you doing?" : reminds me of something else :) Twitter !
Here's my Plazes profile.
By the way, reviewing the site again just now:
1) the URL for my page should have my name in it, not just numbers
2) invite friends needs a major update : use email contact lists like Jaiku for example
b. but it also now has features that remind me of Dopplr ! (future events!)