A few more notes that might help someone…
I installed the binary version of ImageMagick from imagemagick.org into /opt/ImageMagick-6.2.5. I created the symbolic link from /opt/ImageMagick-6.2.5/bin/convert to /user/bin/imconvert, as specified in the Alfresco readme, and I set DYLD_LIBRARY_PATH in my user's .profile. All well and good, but I'm starting Tomcat via sudo and my environment variables are not being passed along. So I added a line to the top of the alfresco.sh script:
. ~janine/.profile
The dot command sources the referenced file and the env variables are thus available when Tomcat starts up. This got rid of the ImageMagick errors, finally.
My final error to deal with was this one:
17:03:57,265 ERROR [org.alfresco.smb.protocol] CIFS server configuration error, Failed to determine local domain/workgroup
I have not, so far, figured out how to get rid of this. I saw the other post about editing file-servers.xml, but I can't find a value for host that works. I tried "localhost_H", and I also tried replacing localhost with the machine's short name and with the full name including domain. Same error each time (I did restart after each change).
Suggestions on how to fix this welcome.