For example the recent Moodlemoot in the UK used #mmuk09 ... and thus you can easily find related messages on Twitter, photos on Flickr and so on.
The only problem is that this tag was not consistent with any other moots. A consistent scheme would make it easier to remember and guess these tags in future, so I'm looking for some feedback/improvement on this simple scheme:
For conferences, use mootCCYY where CC is a country or state, and YY is a year. My reasoning is that "moodle" is a bit long here (remember people are typing on phones etc), and a Moot is not necessarily just about Moodle. The two letter code would usually be a country, but for somewhere like the US where there are different moots they could choose to use "us" or a state like "sf" or "ok". It really wouldn't even matter if two moots both used mootus09, because they would be seperated in time.
For general moodle stuff, use moodle. Obviously.
Does this make sense?