Funny. I'd been watching the "when is twitter going to get groups" conversation for a long time, and turns out your the president. I'm emailing you this because I felt the other "answers" fell short and you might no longer be following the topic.
In Twitter Settings>Notices>@Replies you can select "@ replies to the people I'm following".
If we could have this be the default behavior for all new users, and encourage existing users to change to this setting, the following solution could work:
For most of these conferences there will already be an "official" twitter account, for instance @podcampaz
If I create a message and direct it to @podcampaz only people who also follow @podcampaz will have it show up in their feed. Of course if you went straight to my page, you will see the tweets, so it's not "private" and if you wanted to hear what was going on at PodCampAZ even if you weren't there you would subscribe to them.
(Props to @cycomer for the idea)
If you wanted, you could even make groups like @phoenix @arizona @phx @phxNightLife @phxWork @smith123Family @youtube @RT @OH @twitpic @WolfParadeFans @SpencerKrugFans @WorldOfWarcraftPlayers
Maybe this is an alternative to #
I'll explain by example:
I follow PersonA and PersonB
I don't follow PersonC
Whenever PersonA or PersonB says: Hello World
I see it.
Whenever PersonA @ messages PersonB like: @PersonB I like cupcakes
I see it, because I also follow PersonB
Whenever PersonA @ messages PersonC: @PersonC I'll be in your town next week
I don't see it, because I don't follow PersonC
Now if I go to twitter.com/PersonA I can read all of the messages, but I won't have the @PersonC messages in my feed.
So as an example, I go to @phx2600 meetings, and I live in @cityofchandler. Assuming everyone who lives in Chandler follows @cityofchandler, and everyone who goes to the local 2600 meetings follows @phx2600, AND has @ replies to people they don't follow turned off, I could say:
@phx2600 meeting is tonight. I'm going to bring a box of junk and give away whatever I have, if you are late bring donuts.
and then right after that say:
@cityofchandler there is a broken water main at Kyrene and 56th st, but 58th is packed to, so if you are headed that way, take 60th st
If you only follow @phx2600, you only get the first message.
If you only follow @cityofchandler, you only get the second message.
If you follow both, you get both.
And if you follow neither, (like my dad in another state), you don't see either message.
And everyone sees my: w00t, I just got paid today! Now who do I owe money to?