Here are a couple of things that I've learned specific to your questions. They're sure no book, but I don't think that a practical guide exists. Being good at conferences is as individual as writing code - it's an extension of yourself.

- how to get in and out of a conversation circle

If people are heavily engaged, this is very difficult and you can easily step on the toes of the folks engaged in conversation. Generally, as long as the conversation doesn't "feel" private, stand near the circle and nod a lot. Then, when you have something truly intelligent to add, offer that up. Instantly, you will then be part of the conversation. If you don't have an intelligent part to add, don't. Use this opportunity to break into another group by saying "Bill over there was just talking about tktkt, what do you think of that?"

- event invitations: when is it ok to go and not go

Private events are not ok. Don't show up at the bar or otherwise crash it. Get on the list and do it the right way. At some large, stupidly exclusive events such as Ted, it's ok to show up in the hotel bar and mingle with the folks who paid to be there.

- what's the appropriate amount to talk about yourself and your idea

I use personal information to engage others to talk about themselves. I don't directly talk about myself. A natural part of conversation is to engage people personally in a back-and-forth manner. However, if someone talks about their office in San Francisco, exchange a fact about yourself that involves the area. Use tidbits of information about yourself to engage, not fill conversation. When asked, answer every single personal question honestly and deeply. This goes a long way to developing a relationship. It is however handy to have a few interesting, entertaining stories about yourself. This makes for great dinner conversation where back-and-forth often turns into somewhat of a round-robin of stories.

- how to identify this conversation is going nowhere

I never assume that a conversation isn't going anywhere. One of my biggest pet peeves at conferences are folks who are only there to talk to the heavy hitters. I get wanting to maximize your time, but understand that no single group of people or individual is as valuable as the collection of people attending a conference. There are usually very large brain trusts at events and if you can get a feel for the entire crowd and even have a set of questions answered by a variety of people, this is the best case scenario. Remember that conversations have a natural arc. If you feel stuck in a conversation, you need to learn how to naturally arc the conversation earlier so that you can gracefully move without being noticed.

- how to approach FAMOUS GUY

Remember that you likely won't actually have a discussion with famous people at events. Famous folks (no matter if they're on the bill or not) talk to a lot of people at events and the chance of you gaining any insight or that they will even remember you after you walk away is negligible. My best advice is that if you have some business with someone famous to walk up to him or her after he or she is done presenting, when you notice that they have a quite moment or if all else fails after they come out of the bathroom (never while in the bathroom). Quietly but confidently say something like "Hi Jimmy, my name is John, I know this isn't a great place to talk, but I've come here just to introduce myself in the hope that we can talk again. Here's my card with a note on the back about what I want to talk about. Could you give me a call when you have time or could I call you?"

- how to appropriately ask your friend to introduce you to his friend, FAMOUS GUY

I wouldn't sweat famous people too much. Sure, they look cool and have cool people around them, but for the most part, they're just people with more money then you. The real question that you should be sweating over is, what are you going to do so that people want to be introduced to you? It doesn't matter if your friend knows a music legend or is dating a model, people are people. If you hang around the right people enough, you'll get to know famous people without trying. Specifically at conferences, I'd think carefully about how much value waiting in line (and there is always a line) to talk to someone famous is. Personally, I'd rather talk to everyone in that line and everyone else at the event and then, if need be, talk to the famous person outside of the busy event to connect some dots.