I'm doing a little brainstorming to properly secure my app specifically made for tor.

I notice vidalia has a new identity button. I pressed it and couldn't tell what it did. While looking at the network view i saw a few connections get closed (but not all) and that was about it.

It appears every TCP connection creates a new circuit. Is this right? Does this mean every connection i make cannot be associated with another?

Finally my last question related to identities is. If a client connects to a hidden service many times is it possible to discover who he is? Perhaps by using timing attacks, cookies, looking at IPs connected to the network etc? Where can i read about it? I don't believe relays know when clients connect to the network unless the client connects to the relay as its first node (is that relay called an entrance relay?)