#tags are important to use into tweets but more important is the quality of tweet and the knowledge you share with your followers. You can use maximum 2 #tags in 140 character tweets. If you cross this limit, quality of tweets should be going down and not up to mark.
Also have a look at the quality of the hashtags that you are using.. How many people are using this hashtag? How many people will be searching for it? Quality > Quantity always.
Research what tag would be most useful. People search by tags, so having one in there is a good idea, but I definitely don't recommend more than two. Keep it to 1-2 relevant tags that will get people looking at your tweet.