I don't use an excerpt plugin. I just modify the theme files directly (replacing the_content(); with the_excerpt(); as needed), use the Category Base Killer plugin to re-write my category URL files (since hacking the core files directly isn't very reliable), and disable access to my archives and tags via my robots.txt file. That's really about all you've got to do.
Wordpress does not do very nice excerpts by default though, and many times these plugins can add that extra bit of professionalism.
I use <!--more--> when appropriate. I didn't like any of the plugins I tried out, but that was a while ago. Rich