Blogger tweets. That is Blogger, the blogging platform that I use, has a presence on Twitter now. I can't link to the tiny blog post — AKA tweet — that I've just quoted, but I can link to the announcement, which is titled: "Blogger in 140 characters or less."
The less/fewer distinction is popular with grammar sticklers — the anti-split-infinitivians — but I think more sophisticated grammarians would approve of that post title. It's colloquial and even preferable to say, for example, "Write an essay in 100 words or less." If you say "fewer," you seem like a non-native speaker who is consulting a rule before speaking. Any English speaker with even one ear knows to say "I have less than $100" and "We've got less than 20 minutes before the store closes."
The only reason why "Blogger in 140 characters or less" could be considered wrong is because in Twitter, when you're writing your post you see a countdown from 140, and you know that if you go into the negative numbers, your post won't publish. So there is as distinct particularity to the individual items in the whole mass.
Nevertheless, I say the original title was grammatically correct.