Yes, I mean that. you're looking for characters a-z so if there would be a capital letter, it would break linkification.  also for allowable characters in urls, you also need to add # @ % ; : ! |

There are probably more, but those are the ones I can think of.

Example for @ flickr urls: http://www.flickr.com/photos/99669627@N06/9417403305/in/photostream/