It can be overused for ridiculously narcissistic reasons, BUT ...
It is very useful in public emergency situations, and for broadcasting things like traffic alerts. For instance, if one person gets stuck behind a wreck on the way to a ball game and tweets that on the account for the team, then other people who are headed that way will know to take an alternate route.

I follow two accounts that monitor traffic in my area; they send out tweets when there are wrecks, construction or anything else that causes backups or detours. Yesterday I knew to be in the right lane when approaching our mall because there was a couch in the left lane. I cruised by while a bunch of people got stuck in the lane behind the couch!

My husband changes his route to work some mornings because of the traffic updates and his commute is much more predictable now; it used to vary quite a bit based on traffic.
I follow our local news stations as well as several national news outlets, and I get breaking news far faster through Twitter than any other way.
I follow a few companies I like and get all sorts of coupon codes from their Twitter accounts. (Many of them do the same thing through Facebook, but often they have Twitter exclusive codes some days and Facebook exclusive ones other days.) I've also been to a few "Tweetups" thrown by restaurants, where they give free food and drinks to Twitter followers on specific days. NASA has even had a few Tweetups, and people who went to one of those got to attend a Space Shuttle launch!
I also follow our local utility company. Now when our power goes out I just check Twitter and most of the time I can see why it's out and how long they expect it to be before it comes back on.
I complained on Twitter once about a problem we were having with my mom's insurance company, and had a response from their social media representative within minutes.
I follow several Orlando area feeds, and I find out Disney, Seaworld and Universal news (and wait times) way before I ever see them pop up anywhere else.
Aside from all those I also follow some game companies and authors, musicians, TV shows, websites and even normal people. I haven't found any of them to be narcissists, and hopefully my followers don't think I am, either.
Thank you so much for all the information. I think many of you posted about what I was afraid it was... information on who was at the grocery store when....
Another stupid question....
So it's not really like you can have a conversation with someone on there then?
The only time I ever see anything about people being at the grocery store is if they happen to be playing FourSquare, but of course people play that on Facebook, too. I think if that's the only sort of thing you see on Twitter, you're following the wrong people!
You can have converstations on there, though. If you and I were following each other on Twitter, we could talk to each other. For example, I'd Tweet
@Shmily1, how'd your interview go? and you could reply
@Skurvy I got the job! The only people who would see those tweets would be you, me and anyone else who follows both of us, who then might respond to congratulate you. If you don't want anyone else to see a message you've sent to a specific person, you can send it as a Direct Message instead.
Twitter definitely isn't for everyone, any more than anything else, but those who avoid it because they think it's just a bunch of people talking about going to the grocery store just haven't learned the best way to use that form of social media.
ETA - A few reasons Twitter might be used instead of personal texts: I know a couple of Dissers on Twitter. We talk on there but not in real life. We aren't at the point where we would exchange phone numbers, so Tweets are one way we communicate away from the Dis. Also, Tweets are a good way to include your other friends in the conversation, as with the interview example, without bombarding them with texts. Plus some people don't have unlimited texting, and Twitter is free.
