What are #hashtags and when is it appropriate to use them on Twitter?
Hashtags should be used to thread a conversation together or to provide context. Hashtags used as popular keywords is a marginal tactic and can be perceived as desperate or trying too hard.
Example 1: If I used the tag #onlinemarketing after every tweet, it would seem gratuitous.
Example 2: If I tweeted a question about opinions on Facebook Like buttons, I might add the tag #pollfblike to my original question so that replies might also use it to string the responses together.
Example 3: If I tweeted a statement, observation or quote about strategy, I might add the tag #socialmediastrategy to provide context.
Hashtags have been used effectively to conduct scheduled conversation on Twitter such as #blogchat or #journchat. A blog or Facebook Fan page typically announces the scheduled chat and topic on Twitter along with a designated hashtag. That same blog might also aggregate all the messages for the discussion for easy consumption later. The compilation of tweets also provides great content for search engines.