It's php code and not a physical link on the sidebar template page, so how do you go about making this link nofollow?
There is a file in the wp-include that you can change this information (in the meta widget). I already did this, but don't remember exactly. Just search all files in wp-include (one editor freeware i use that make this, search all files in one time, is crimson editor) and you will find. Maybe you can retire from your page the meta widget, and when you want login just add /wp-admin in your url bar.
I always like to remove the link completely and bookmark the admin page, it gets rid of an unrelated keyword, cleans up the template plus other search engines and bad bots disregard Nofollow. But, read this: http://holbreich.de/2008/02/mark-meta-widget-with-rel-nofollow/
Not only that, but people will also look for things like WordPress login pages so they can try to compromise the system. I try to hide the fact I'm using WordPress as much as possible in most cases, even going so far as to use mod_rewrite to literally rewrite the links that point to my WordPress theme and include files (oh, and my admin directory too).
Very helpful man. I prefer to keep the login page link on the site, I hate referring to bookmarks all the time.
No problems, that's why i thought i would throw both solutions out there. I'm like Dan, i don't like having private logins public and i like to remove standard footprints from CMS's that people use to find your site to monkey around.