i’ve seen GCALDaemon before but i never really paid any attention to it until i saw a lifehacker post that mentioned it could sync your google contacts with a local mail client. gcaldaemon is a java program that runs server locally on your box which acts as a middle man so you can pass messages from evolution (or any ical client) and google calendars.
installing gcaldaemon on linux is pretty straight forward, and the gcal-daemon.cfg config is well commented and easy to edit. the gcaldaemon site has a howto for setting up evolution to use gcaldaemon. there’s also a howto for accessing gmail contacts in thunderbird. i never did get the google contacts working in evolution but i do have the calendar sync working.
if you want a non-read only google calendar sync with evolution and you don’t want to install/configure gcaldaemon you could always just wait a little longer. it looks like evolution 2.21.1 will have native 2 way sync with google calendars using a new Gdata library. hopefully the library will also add support for contacts and email, not just calendars. oh, and other linux applications should be able to use the Gdata library also… i’m half tempted to go grab the svn version of evolution and compile it myself.