New York Times social media editor Daniel Victor argues that the oft used Twitter hashtag is mostly visual noise. Using #superbowl as an example, Victor points out your #superbowl hashtag was one of 3 million used in a five hour period. So it didn't likely get noticed. The more popular the hashtag, the less effective it becomes.
But what's the harm you may ask. Victor's response is pretty funny.
"Using a hashtag does no harm in the same way wood paneling does no harm to your station wagon, or a misspelled tattoo does no harm to your bicep."
Victor calls hashtags "aesthetically damaging" believing they are less likely to be retweeted.
But there are good uses for hashtags as Victor admits. They work well for smaller groups and subtext.
Regarding best practices for professionals, Victor makes some good points. As for the rest of Twitter users, I suspect most use hashtags more often than not to feel they are part of something larger.