Sure, but the relatively short link to your reply, http://news.ycombinator.com/item?id=2492783, is already 44 characters, so I'm only left with 96 characters on a twitter message.
With bit.ly, the link is much shorter with 21 characters, http://bit.ly/j8IpC8, and I'm left with 119 characters to describe the link in a twitter message.
Oh, and I'll know how many people clicked on my bit.ly link. I've become addicted to that feature.
Yes it is pretty much an artificial problem created by an arbitrary limit.
It would be better if Twitter offered their own way to shorten URLs (or have a separate limit for URL length), so that you could still see where the link pointed before clicking on it.
If you use the Tweet button, either embedded in a page or installed as a bookmarklet, it will run through Twitter's own shortener. A long version of the URL will then be displayed in the Twitter UI.