Many conferences and events follow a simple principle. They use a short tag for twitter (e.g. #dpc) and a full tag for less real-time content (e.g. dpc09 on Flickr or blogs). It's not a rule that's set in stone, but it kind of emerged as a best practice based on people's experiences. Other conferences stick to one tag, such as "phpuk2009" last friday.

For those that don't adhere to this best practice, here are the most important reasons for doing so:

• You only have 140 chars on Twitter. The shorter your tag, the more actual content you can add.

• Many attendees use a phone to tweet, and many phones use a T9 editor. Again, the shorter the better. Also, entering a year such as '2009' not only requires 4 key presses, it requires 4 'hold' keypresses on many phones, or it requires the T9-editor to be set to numeric mode first.
• Findability. This morning I was trying to find blogs and pictures from #phpuk2009. Because the same tag was used on all media, the blog posts were hard to find between hundreds of tweets in the Google results. While it's interesting to find those as well sometimes, their real-time nature makes it much less interesting as a search result once the event is over (and it's far more easier to use search.twitter.com to view them in the correct order.

To sum up a few counterarguments:

• When you search it's hard to distinguish between different installments of the event. While I'd say that in blogs and Flickr and other things you would search through Google that is true (I recommend always adding '09' to tags there), for Twitter that is not an issue, because your search is always in order of date anyway.

• "I have phone X, it's really easy to add the year to any tag." Sure, but not everyone has phone X.
• For conference organizers, it's harder to scan the web for relevant content if different tags are used. Actually that's not the case: it's easier to find relevant non-realtime content and relevant realtime content when 2 different tags are used. See 'Findability' above.

There is a group of people that takes this a step further; they argue that a date should never be added to any tag, because appending a separate year tag makes it much more flexible (e.g. #dpc #2009). That's an interesting approach too, but makes it slightly less convenient for my taste (and generally requires even more characters), so I'll stick to #short for real-time content and #full09 for normal content.

What do you think?