To get back to the topic, Ive always wondered how much time you actually get to say anything to the actors at these conventions. Don't you only really get a few seconds when they're signing stuff for you?
It depends. At the large corporate-type conventions generally yes, you may only get a minute or two (or less) to chat with an actor. However even at those cons at certain times the lineup for an actor can be really small and you could get a chance to talk to them for a while. To some extent the length of a lineup for an actor can be connected to how long you can talk with them, and then there are some actors that will talk to you for a while regardless of how long the line is--I remember a huge line for Mary McDonnell from BSG yet she still took the time to talk to everyone for a while.
At the smaller cons the actors will sometimes hang out with fans and if there's a bar or something in the hotel you could end up having drinks with them. As I mentioned earlier in the thread, Michael Hogan of BSG hung out with us and we got our drunk on. Kai Owen (Rhys) from Torchwood was just hanging out at the bar at one con I attended, he came over and actually initiated conversation with us as opposed to the other way around. The next day we had drinks with him before his Q and A session, he remembered us from the night before and invited us over--granted he doesn't have the 'star power' of a Shatner or Nimoy but he was a really funny and warm individual.
Some cons also have 'exclusive' meet and greet events where a limited number of people can mingle with the actors, but those type of events you have to pay extra for.