The best part of being in fandoms is definitely when you're acutely aware of the community you're a part of. I think that comes out in conventions more than anything else for most fans. I know the one year I was able to go to LeakyCon (maybe, hopefully, there will be a future time) was one of the best times of my life for that very reason. I had never felt as much a part of the Harry Potter fandom as I did that weekend while in one giant ballroom-wide group hug at the end of a Harry and the Potters set. That moment is one I will never forget even though it was hectic and crazy and one of those moments where you're just so amazed that it's happening to you that you're having trouble even taking it in.
I haven't had many moments like that. The only thing close to that for me with other fandoms are concerts. Concerts are a lot different due to the atmosphere though. Typically they're more about the people on stage than the people around you, which definitely sets conventions apart. It's a shame really because I think concerts could be a great time to bond with people around you due to having at least one interest in common. (Although, I fully acknowledge that different concerts have very different atmospheres, and my big moment above even happened at a wizard rock concert that just happened to be at a convention. It all depends.)
Don't get me wrong, there are a lot of moments with fandoms that happen online that make me feel all warm and fuzzy and like I'm just in a great community too. (And bad times, but I'm not focusing on that at the moment.) There's something really great about in person moments though.
I'm definitely having one of those times where I get really sentimental about LeakyCon 2011. Most of the time I forget I even went because the entire thing feels like a dream to me. If I do get to go to another convention, it won't be soon, but I guess I'm at least lucky enough to have those memories now.