I already once posted this in my Blog some time ago, but recently found out, that the previously used solution with TwitThis.com doesn’t work anymore and even got a bit “suspicious”. In the meantime, Twitter is offering it’s own “Tweet this” popup window. I made use of this feature now for a shortcut button in the Safari bookmarks bar.
Thanks to the built in shortcut feature in Safari, you may use Command+[Number] to directly fire this new bookmark from within the bookmarks bar. In my example it would be Command+5 (the “-> Tweet this” button is at the 5th location in the bookmarks bar).
So here is the screencast with the How-to:
By the way: this solution should also work on other web browsers such as Firefox or Chrome! Haven’t tested it though.