There is a popular opinion by many who don't use it that Twitter is a waste of time.
The same can be said about any social networking site when you think about it.
People who don't use them tend to think that they are a waste of time and the people who do use them seem to have their reasons behind why they do.
As for the question of whether or not Twitter is a waste of time, it comes to the individual.
What are you using it for? What types of benefits do you hope to get from it? Many people find it helps them socialize, many more money, promote their business or company, promote a products or service and more.
In cases like this, it's not a waste of time because it's bringing something beneficial to the user.
Then it's also important to note that it's possible to have too much of a good thing.
If you're spending so much time on Twitter you're not getting other responsibilities done or you are sacrificing real face-to-face human contact then it might be to time to reconsider how much and if you use it at all.
The real answer to whether or not Twitter is a waste of time is up to the individual.
If you think you're getting results from it- whether personal or business- then there is no reason not to use it.
If it's not benefiting you in any way or it's more work than you reap rewards, then maybe it is a waste of time for you.
The potential is there if you use it properly however, for Twitter to be a great asset to any individual or business.