UPDATE: I’ve corrected some misinformation in the original post. Thanks to @WebTrawler for pointing it out. I should have known better. Twitter long ago announced they were going to do it this way, but they changed how things displayed, and it fooled me! My apologies.
Most tweets with links will be shorter/get more characters
Most URLs will be shortened in such a way that you get more characters than 140 for what you type. But some will not, because Twitter isn’t actually counting what you see. Here’s what’s happened:
As part of Twitter’s new automatic link shortening service (on #NewTwitter), it will often remove the http:// from your links and still show the result as a clickable hyperlink. So, for example
This means that any tweet with a link tweeted from Twitter.com (and eventually, elsewhere) seems to save 7 characters by removing the “http://”
What really happens
But actually, Twitter does NOT count what you see. It converts all URLs to t.co URLs even if it shows you something else. And Twitter counts the length of the t.co URL, regardless of what is displayed!
So http://j.mp/123456 (19 characters) is displayed as j.mp/123456 (12 characters, appearing to save seven characters) but is counted as http://t.co/Xh8YoOk (20 characters) so you actually lose 1 character.
Who saves the most?
So if you’re using a non-shortened URL (such as http://blog.tweetsmarter.com/) the new URL shortening will save you a lot of characters. But if you’re already using a shortened URL, it’s going to make very little difference, and could end up costing you characters, rather than saving you characters.
Why does Twitter do this?
Twitter tests all URLs as part of converting them to t.co links in order to try to ferret out malware. In other words, they’re doing it to protect Twitter users—which is a good thing. I would expect that many Twitter clients will also provide this shortening/protecting feature to their users eventually.