I released a new plugin yesterday which you can download here.
The author link from the
template tag on the blog will link to the author’s BuddyPress member profile instead of the author’s posts page. This plugin can be installed in either the mu-plugins or plugins folder.
If you are running multiple WPMU sites in your install, the plugin will not affect the author link on sites where BP is not activated. It is compatible with WPMU 2.7.1 – 2.8.1 & BP 1.0 – 1.0.3.
Edit: this plugin now lives in the repo. http://buddypress.org/community/groups/bp-blog-author-link/